Liquid-crystalline medium for use in a switching element

ABSTRACT

Liquid-crystalline media containing one or more mesogenic compounds, one or more chiral compounds, and one or more polymerizable mesogenic compounds, wherein the media exhibit a pitch of 0.55 μm or more and a clearing point of 80° C. or more and wherein the one or more polymerizable mesogenic compounds are contained in an amount, based on the overall contents of the media, of 5% by weight or less, are suitable as modulation materials. Such modulation materials can be used in switching layers and window elements.

The present invention relates to liquid-crystalline media comprising oneor more mesogenic compounds, one or more chiral compounds, and one ormore polymerisable mesogenic compounds, wherein the media exhibit apitch of 0.55 μm or more and a clearing point of 80° C. or more andwherein the one or more polymerisable mesogenic compounds are containedin an amount, based on the overall contents of the media, of 5% byweight or less. The present invention further relates to modulationmaterials obtainable from the media and to switching layers and windowelements containing the materials.

Optical intensity modulators such as light shutters can be based onliquid crystals (LCs). In principle, such light shutters may rely on thescattering of light or the absorption of light. LC-based light shuttersusing light scattering include so-called polymer dispersed liquidcrystal (PDLC), polymer network liquid crystal (PNLC) and cholestericliquid crystal (CLC) devices. These scattering-type devices can beswitched between transparent and translucent states.

LC-based light shutters or modulators can be used as switchable windowsfor automotive and architectural applications, wherein a light shutteror light modulator operating in the scattering mode can in particular beused as a privacy window. Light scattering may also be useful inreducing glare or dazzling from direct sunlight irradiation.

Switching between states may e.g. be thermally controlled. However, inmany cases it can be suitable and even advantageous to use electricalswitching. When a device is switched from a non-scattering state to ascattering state, the transmission of light is changed such that atranslucent appearance is produced, which may also be perceived ascloudy, turbid, diffuse, hazy or opaque.

WO 2016/173693 A1 describes a switching layer comprising aliquid-crystalline medium for use in a switching element which hasforward-scattering properties in at least one of the switching statesand which facilitates switching from a transparent state into atranslucent or opaque state.

WO 2009/151716 A2 describes a switchable liquid crystal window based ona bistable dual frequency polymer stabilized cholesteric liquid crystalmaterial, wherein the liquid crystal material is switched from atransparent state to a light scattering state upon application of avoltage pulse having a first frequency and from a light scattering stateto a transparent state upon application of a voltage pulse having asecond frequency.

In WO 00/60407 A1 electro-optical glazing structures are described whichhave scattering and transparent modes of operation.

There is a need in the art for liquid-crystalline media with improvedchemical, physical and electro-optical properties, in particular for usein switching elements and window elements. Furthermore, there is a needin the art for switchable devices which can provide suitable scatteringwith a uniform appearance for privacy applications, which can beoperated at suitably low voltages and low energy consumption, and whichcan have suitable reliability and stability, e.g. with respect toelectrical breakdown and light stability.

An object of the present invention is therefore to provide switchabledevices, in particular window elements, having good stability, e.g.against electrical breakdown, and a favourably low operating voltage orlow energy consumption and which can show adequately efficient andsufficiently uniform scattering. It is another object to provide anefficient and facile process for preparing such devices.

It is a further object of the present invention to provide improvedliquid-crystalline media and modulation materials which in particularexhibit good reliability and stability, in particular light stabilityand especially UV light stability, and a broad liquid-crystalline phasewith a suitably high clearing point and which are particularly useful inswitching elements and window elements, especially switchable elementshaving a scattering mode. It is furthermore desired that theliquid-crystalline media have sufficiently high optical anisotropiestogether with a favourably high voltage holding ratio (VHR), goodlow-temperature stability and suitable stability for storage. Furtherobjects of the present invention are immediately evident to the personskilled in the art from the following detailed description.

The objects are solved by the subject-matter defined in the independentclaims, while preferred embodiments are set forth in the respectivedependent claims and are further described below.

The present invention in particular provides the following itemsincluding main aspects, preferred embodiments and particular features,which respectively alone and in combination contribute to solving theabove objects and eventually provide additional advantages.

A first aspect of the present invention provides a window element, whichis operable in and electrically switchable between an opticallytransparent state and a scattering state and which comprises a switchinglayer containing a material which comprises

-   -   a liquid-crystalline medium comprising one or more mesogenic        compounds and one or more chiral compounds, wherein the        liquid-crystalline medium has a clearing point of 80° C. or        more, and    -   a polymeric component comprising one or more polymeric        structures obtained by or respectively obtainable from        polymerisation of one or more polymerisable mesogenic compounds,        wherein the polymeric component is contained in the material in        an amount, based on the overall contents of the material, of 5%        by weight or less.

According to the invention advantageous window elements are providedwhich can be used in switchable windows for automotive and architecturalapplications, and which are particularly useful and efficient inproviding a privacy mode when desired, i.e. they offer switchabilitybetween a state with viewing contact and a private state giving a visualbarrier. Furthermore, the switching can be fast and the window elementmay be installed with minimum space requirement, which can offersignificant advantages, e.g. in comparison to traditional awnings orblinds.

The window element according to the invention is useful for regulatingor modulating the passage of light, in particular the passage ofsunlight but also of light from artificial light sources like lamps andlight fixtures.

The window element according to the invention may advantageously beemployed in a window of an external facade, but also in the inside ofrooms, for example in dividing walls between rooms and in elements forseparating individual compartments of rooms or spaces. In this case theprivacy which is achieved by switching the window element from clear toscattering can produce a visual barrier between the different parts ofthe room.

According to a preferred embodiment the liquid-crystalline medium whichis comprised in the material contained in the switching layer of thewindow element exhibits a pitch of 0.55 μm or more in the scatteringstate.

It has surprisingly been found that an improved device can be obtainedby including a switching layer in the window element which contains amaterial which comprises the liquid-crystalline medium and the polymericcomponent as set forth above and below. In particular, providing thecholesteric or chiral nematic medium having a high clearing point and along pitch as presently defined in combination with a relatively smallamount of a polymeric component which includes polymeric structuresobtainable from polymerisation of at least one polymerisable mesogeniccompound can surprisingly give a device which has a favourable clearstate, i.e. a favourably homogeneous low haze and optically transparentstate, as well as a scattering state having an enhanced scatteringefficiency together with a homogeneous and colour-neutral appearance,wherein the device can be conveniently switched between the states byapplying an electrical voltage.

In particular, the combination of the long pitch cholesteric medium withthe presence of the polymeric component as herein described can giveunexpectedly strong scattering with a suitably broad angular scatteringdistribution. This is beneficial in that already the provision of only asingle switching layer in the element can result in a suitable privacymode. In addition, the thickness of the switching layer may becomparatively low, in particular substantially below 35 μm, which thusreduces the operating voltage and power consumption but also the use ofmaterial.

Therefore, according to the invention a switchable window element forprivacy applications can be obtained which has both an advantageous lowhaze clear state and an advantageous opaque state with sufficientlyuniform scattering wherein unwanted colour effects are favourablyavoided or minimized. In addition, the device can provide furtherbenefits such as good reliability, durability and stability, e.g. withrespect to electrical breakdown and light stability, in particular UVlight stability, as well as a favourably low switching voltage and lowenergy consumption.

Another aspect of the invention relates to a method for preparing awindow element, comprising (i) the provision of a liquid-crystallinemedium which comprises one or more mesogenic compounds, one or morechiral compounds and one or more polymerisable mesogenic compounds as alayer between two opposing transparent substrates which are eachprovided with an electrode, wherein the liquid-crystalline medium has aclearing point of 80° C. or more and exhibits a pitch of 0.55 μm ormore, and wherein the one or more polymerisable mesogenic compounds arecontained in the medium in an amount, based on the overall contents ofthe medium, of 5% by weight or less, and subsequently (ii) carrying outpolymerisation of the one or more polymerisable mesogenic compounds inthe presence of an applied electric field in the layer.

Surprisingly, this method provides a facile and efficient process toprepare the window element which exhibits the advantageous properties asdescribed herein.

Therefore, in another aspect of the invention a window element for themodulation of the passage of light is provided, wherein the windowelement is obtained by or respectively obtainable from carrying out themethod as described above and below.

Another aspect of the invention relates to a liquid-crystalline mediumwhich comprises one or more mesogenic compounds, one or more chiralcompounds, and one or more polymerisable mesogenic compounds in anamount, based on the overall contents of the medium, of 5% by weight orless, wherein the medium exhibits a pitch of 0.55 μm or more and aclearing point of 80° C. or more.

It has surprisingly been found that by providing the liquid-crystallinemedium according to the invention a medium with improved properties, inparticular a suitably high clearing point and a suitably long pitch, canbe obtained which is particularly useful for preparing modulationmaterials for switching layers and window elements. In addition themedia can provide further benefits such as a suitably high opticalanisotropy, a favourably high voltage holding ratio (VHR) and good lightstability.

In a further aspect of the present invention there is provided amodulation material which comprises a liquid-crystalline mediumcomprising one or more mesogenic compounds and one or more chiralcompounds, wherein the liquid-crystalline medium has a clearing point of80° C. or more and exhibits a pitch of 0.55 μm or more, and whichfurther comprises a polymeric component comprising one or more polymericstructures obtained by or respectively obtainable from polymerisation ofone or more polymerisable mesogenic compounds, wherein the polymericcomponent is contained in the material in an amount, based on theoverall contents of the material, of 5% by weight or less.

The modulation material according to the invention can be beneficiallyused in switching elements, in particular in switching elements andwindow elements based on the scattering of light. The modulationmaterial according to the invention is preferably used in devices forregulating the passage of electromagnetic radiation, preferably light,and in particular sunlight but also light from artificial light sources.

It is particularly preferred that the modulation material according tothe invention is used in CLC scattering-type devices. It has presentlybeen recognized that particular benefits, e.g. in terms of scatteringefficiency or uniformity and appearance of the scattering effect, can beobtained when the material contains the chiral nematic or cholestericliquid-crystalline medium which has a relatively long pitch and afavourably high clearing point in combination with the polymericcomponent as presently defined, and in particular when a so-calledpolymer stabilized cholesteric texture (PSCT) is provided.

According to the invention the liquid-crystalline medium and themodulation material as described herein can be beneficially arranged andused in a switching layer. In a further aspect there is thus provided aswitching layer which comprises, preferably consists of, the medium orrespectively the material according to the invention.

The switching layer can be arranged between two substrates such as togive a switching element which is electrically switchable and operablein an optically transparent state and a scattering state.

Polymerisation stabilization can provide benefits for the scatteringperformance and efficiency in the scattering state, while still allowingto achieve favourable clarity in the transparent state.

Without limiting the present invention thereby, in the following theinvention is illustrated by the detailed description of the aspects,embodiments and particular features, and particular embodiments aredescribed in more detail.

The term “liquid crystal” (LC) herein preferably relates to materials ormedia having liquid-crystalline mesophases in some temperature ranges(thermotropic LCs). They contain mesogenic compounds.

The terms “mesogenic compound” and “liquid crystal compound” mean acompound comprising one or more calamitic (rod- or board/lath-shaped) ordiscotic (disc-shaped) mesogenic groups, i.e. groups with the ability toinduce liquid-crystalline phase or mesophase behaviour.

The LC compounds or materials and the mesogenic compounds or materialscomprising mesogenic groups do not necessarily have to exhibit aliquid-crystalline phase themselves. It is also possible that they showliquid-crystalline phase behaviour only in mixtures with othercompounds. This includes low-molecular-weight non-reactiveliquid-crystalline compounds, reactive or polymerisableliquid-crystalline compounds, and liquid-crystalline polymers.

A calamitic mesogenic compound is usually comprising a mesogenic coreconsisting of one or more aromatic or non-aromatic cyclic groupsconnected to each other directly or via linkage groups, optionallycomprising terminal groups attached to the ends of the mesogenic core,and optionally comprising one or more lateral groups attached to thelong side of the mesogenic core, wherein these terminal and lateralgroups are usually selected e.g. from carbyl or hydrocarbyl groups,polar groups like halogen, nitro, hydroxy, etc., or polymerisablegroups.

For the sake of simplicity, the term “liquid crystal” or“liquid-crystalline” material or medium is used for both liquid crystalmaterials or media and mesogenic materials or media, and vice versa, andthe term “mesogen” is used for the mesogenic groups of the material.

The term “non-mesogenic compound or material” means a compound ormaterial that does not contain a mesogenic group as defined above.

As used herein, the term “polymer” will be understood to mean a moleculethat encompasses a backbone of one or more distinct types of repeatingunits (the smallest constitutional unit of the molecule) and isinclusive of the commonly known terms “oligomer”, “copolymer”,“homopolymer” and the like. Further, it will be understood that the termpolymer is inclusive of, in addition to the polymer itself, residuesfrom initiators, catalysts, and other elements attendant to thesynthesis of such a polymer, where such residues are understood as notbeing covalently incorporated thereto. Further, such residues and otherelements, while normally removed during post-polymerisation purificationprocesses, are typically mixed or co-mingled with the polymer such thatthey generally remain with the polymer when it is transferred betweenvessels or between solvents or dispersion media.

The term “polymerisation” means the chemical process to form a polymerby bonding together multiple polymerisable groups or polymer precursors(polymerisable compounds) containing such polymerisable groups.

Polymerisable compounds with one polymerisable group are also referredto as “monoreactive” compounds, compounds with two polymerisable groupsas “direactive” compounds, and compounds with more than twopolymerisable groups as “multireactive” compounds. Compounds without apolymerisable group are also referred to as “non-reactive” or“non-polymerisable” compounds.

The terms “film” and “layer” include rigid or flexible, self-supportingor freestanding films or layers with more or less pronounced mechanicalstability, as well as coatings or layers on a supporting substrate orbetween two substrates.

The term “chiral” in general is used to describe an object that isnon-superimposable on its mirror image. By contrast, “achiral”(non-chiral) objects are objects that are identical to their mirrorimage. The medium according to the invention exhibits chirality. Thiscan be achieved by providing cholesteric liquid crystals, which are alsoknown as chiral nematic liquid crystals. The terms chiral nematic andcholesteric are used synonymously herein, unless explicitly statedotherwise.

Herein

denote trans-1,4-cyclohexylene.

Herein, unless explicitly stated otherwise, all concentrations are givenin weight percent and relate to the respective complete mixture.

All temperatures are given in degrees centigrade (Celsius, ° C.) and alldifferences of temperatures in degrees centigrade. All physicalproperties and physicochemical or electro-optical parameters aredetermined and given for a temperature of 20° C., unless explicitlystated otherwise.

Transmission and scattering of light preferably refers to thetransmission and scattering of electromagnetic radiation in the spectralrange from 380 nm to 780 nm.

Switching preferably refers to the switching between binary states,wherein preferably one state is non-scattering and appears substantiallytransparent or clear to the human eye and another state is scattering orhas diffusive transmission and appears translucent or opaque to thehuman eye.

However, it is also possible for the switching layer according to theinvention to have further switching states, in particular intermediatestates.

Therefore, according to the invention preferably and favourablyswitching between a completely private state and a state with viewingcontact to the exterior or a neighbouring space is obtainable.

In the optically transparent state according to the invention the windowelement preferably has a haze, determined according to ASTM D 1003, ofless than 20%, more preferably less than 15%, even more preferably lessthan 10% and in particular less than 5%.

In the scattering state according to the invention the window elementpreferably has a haze, determined according to ASTM D 1003, of more than75%, more preferably more than 85%, even more preferably more than 90%.It is particularly preferred that in the scattering state the windowelement according to the invention has a haze, determined according toASTM D 1003, of 95% or more.

For the measurement of haze hazemeters made by BYK-Gardner may be used.It is also possible to use spectrophotometers.

Switching according to the invention preferably means electricalswitching. Electrical switching can typically be achieved by providingsubstrates, e.g. glass substrates, with electrodes. In an embodimentelectrically conductive layers are provided on the substrates, whereinthe conductive layers comprise or are formed of a transparent conductivematerial, e.g. a transparent conductive oxide, preferably indium tinoxide (ITO) or SnO₂:F, in particular ITO, or a conductive polymer, or athin transparent metal and/or metal oxide layer, for example silver. Theelectrically conductive layers are preferably provided with electricalconnections. The voltage is preferably supplied by a battery, arechargeable battery, a supercapacitor or an external current source,more preferably by an external current source.

In an embodiment there are provided orientation layers, e.g. made ofpolyimide (PI), on the substrate. It is particularly preferred thatelectrically conductive layers and orientation layers are providedtogether on the substrates. In this case the orientation layer oralignment layer is provided on top of the conductive layer such that theorientation layer is contacting the LC medium. The orientation layers,preferably polyimide layers, may be arranged such that they provide, inparticular at the interface, homogeneous or planar orientation oralternatively homeotropic orientation of the molecules of theliquid-crystalline medium. In a particular embodiment rubbed polyimideis used on both substrates having a difference in direction of 90° asused in the so-called twisted nematic (TN) geometry.

In a particular embodiment alignment layers with pre-tilt angles areused, e.g. having pre-tilt angles ranging from 0° to 20° for the TNgeometry or from 80° to 90° for the vertically aligned (VA) geometry.

Alternatively and according to another preferred embodiment, substrateswithout orientation layers are used. It has surprisingly been found thatthe provision of orientation layers, e.g. polyimide layers, asadditional layers may beneficially be avoided, while effective andefficient switching behaviour may still be realized.

It is also possible to provide passivation or barrier layers on thesubstrates, alternatively but also in addition to orientation layers,e.g. passivation layers comprising silicon oxide or silicon nitride,preferably consisting of silicon oxide or silicon nitride. In case botha passivation layer and an orientation layer are provided on a substratethey are arranged such that the orientation layer is topmost, i.e. iscontacting the LC medium.

In a first aspect the invention relates to a window element, which isoperable in and electrically switchable between an optically transparentstate and a scattering state and which comprises a switching layer. Theswitching layer contains a material which comprises a liquid-crystallinemedium comprising one or more mesogenic compounds and one or more chiralcompounds, and a polymeric component comprising one or more polymericstructures obtained by or respectively obtainable from polymerisation ofone or more polymerisable mesogenic compounds.

According to the invention the polymeric component is contained in thematerial in an amount, based on the overall contents of the material, of5% by weight or less, preferably 3.5% by weight or less, more preferably2.5% by weight or less, and in particular 1% by weight or less. In apreferred embodiment the polymeric component is contained in thematerial in an amount, based on the overall contents of the material, inthe range from 0.5 to 1.5% by weight.

The polymeric component comprises one or more polymeric structuresobtained by or respectively obtainable from polymerisation of one ormore polymerisable mesogenic compounds. It is preferred that thepolymeric component is obtained from polymerising exclusively one ormore polymerisable mesogenic compounds, i.e. that the polymericcomponent consists of one or more polymeric structures which are onlybased on or respectively only derived from one or more polymerisablemesogenic compounds as the precursors. It is particularly preferred thatthe polymeric component is prepared in situ, in particular in theswitching layer, by polymerising one, two or three polymerisablemesogenic compounds, even more preferably one or two polymerisablemesogenic compounds.

Polymerisable mesogenic compounds according to the invention contain amesogenic group and one or more polymerisable groups, i.e. functionalgroups which are suitable for polymerisation. These compounds are alsoknown as reactive mesogens (RMs) or mesogenic monomers. The RMs can bemonoreactive and/or di- or multireactive.

While it is preferred that the polymerisable compound(s) as usedaccording to the invention include(s) only reactive mesogen(s), i.e. allthe reactive monomers are mesogens, in an alternative embodiment it isalso possible to use one or more RMs in combination with one or morenon-mesogenic polymerisable compounds.

The polymerisable compounds and the mesogenic compounds may be chosen inview of matching the refractive indices of the obtained polymericcomponent and the LC medium in the modulation material, which canfavourably contribute to improving the clear state.

According to the invention the liquid-crystalline medium, in particularas used in the switching layer of the window element, has a clearingpoint of 80° C. or more, more preferably 90° C. or more, even morepreferably 95° C. or more, yet even more preferably 98° C. or more,still even more preferably 102° C. or more, and in particular 115° C. ormore. It is preferred that the medium has a clearing point in the rangefrom 90° C. to 160° C. and more preferably from 100° C. to 150° C.

All physical properties and physicochemical or electro-opticalparameters are determined by generally known methods, in particularaccording to “Merck Liquid Crystals, Physical Properties of LiquidCrystals”, Status November 1997, Merck KGaA, Germany.

The clearing point, in particular the phase transition temperaturebetween the chiral nematic or cholesteric phase and the isotropic phase,can be measured and determined by commonly known methods, e.g. using aMettler oven, a hot-stage under a polarizing microscope, or differentialscanning calorimetry (DSC) analysis. According to the invention theclearing point is preferably determined by DSC.

Furthermore, according to the invention the liquid-crystalline medium,preferably as used in the switching layer of the window element,exhibits a pitch of 0.55 μm or more in the scattering state.

The cholesteric or chiral nematic medium as presently provided has arelatively long pitch, and in particular a pitch which preferably givesBragg-type reflection of greater than 780 nm. In this case also theplanar texture may give favourable transmission over the visible lightspectrum.

The pitch herein means the pitch p of the cholesteric helix, wherein thepitch p is the distance for the orientational axis (director) of the CLCto undergo a 27 rotation. In a preferred embodiment the medium exhibitsa pitch of 0.75 μm or more, even more preferably of 1.00 μm or more andin particular of 1.50 μm or more.

Preferably the concentration of the one or more chiral dopants is setsuch that the resulting chiral pitch is in the range of 0.55 μm to 10μm.

According to the invention the pitch is determined from NIRspectroscopic measurement, in particular at 20° C., of the wavelength ofthe selective reflection maximum λ_(max). The pitch p is determined fromthe measured value of λ_(max) using the equation λ_(max)=n(λ_(max))*p,wherein n(λ_(max)) is the refractive index at λ_(max).

It is also possible to use the wedge cell method which is known in theart to measure, in particular at 20° C., the helical twisting power HTPand to confirm the determined the pitch.

Surprisingly the window element according to the invention can beswitched to and operated in a scattering state which gives efficient andsufficiently strong scattering, in particular diffuse transmittance,with a homogeneous appearance to the eye, in particular over large areasas is desirable for larger windows. This uniform appearanceadvantageously includes a colour-neutral appearance, which means thatundesirable colour effects or respectively colour artefacts can beminimized or even avoided.

It was recognized that in a layer containing a cholesteric materialcolour effects may occur due to the inherent chiral periodicity, e.g.different colours may be transmitted under different angles when thematerial is illuminated with direct, non-diffuse light. In such a casethe transmitted light is coloured when observed off-axis and a windowelement and the window may appear coloured when observed off-axis,wherein the observed colour depends on the angle of observation. Thiseffect may give a resemblance to a rainbow-like appearance. It wasfurther recognized that in many applications such colour effects areundesirable.

It is believed that the material as provided in the switching layeraccording to the invention can give sufficient scattering with thedesired haze, e.g. by scattering from the material domains, inparticular from boundaries, defects or random structures, whereasdiffraction of incident light as caused by periodic structures may besubstantially suppressed or avoided by sufficiently perturbing ordisrupting the periodicity on the relevant length scales, in particularby the introduction of the polymeric component, which surprisingly maybe effective in this regard even when contained in only small amounts.

The window element according to the invention allows light to passthrough it. It can be favourably used and included in windows, glazingunits, including insulating glazing units, facade elements, roomdividers, separating walls and the like and it can be used therein asthe element which provides a switchable privacy mode on demand, whichcan alternatively or in addition also provide anti-glare control.

The window element as a switchable scattering cell or device can be usedto regulate or modulate the passage of light from an exterior space intoan interior space, e.g. into the interior of a building such as aresidential building, an office building or a building used forcommercial purposes, or vehicles. The window element can also be used toregulate or modulate the passage of light from an interior space intoanother interior space, in particular in structural elements whichseparate different functional areas or rooms, where in at least one ofthe spaces a privacy mode which blocks direct viewing from the otherspace is desired temporarily, i.e. only for given periods of time butnot for others.

In an embodiment a window is provided which comprises the window elementaccording to the invention, preferably for interior applications. Thewindow element may suitably be integrated into the window, for exampleby lamination or gluing, preferably lamination to panes or glazingunits.

The window elements and also the windows as a whole which include thewindow element preferably do not comprise any light sources. Thus, anylight transmitted through the window stems from an external light sourcesuch as the sun or a home lighting apparatus.

The window element preferably has a size of greater than 0.5 m², morepreferably greater than 1 m², and even more preferably greater than 3m². In an embodiment the window element has an area in the range of 0.25m² to 15 m², and more preferably in the range of 0.5 m² to 10 m².

The window element may have different shapes, e.g. square, rectangular,triangular or polygonal.

Preferably the window element and the window contain no polarizer.

According to the invention the state of the switching layer and thewindow element is controlled using an electric field which is applied bymeans of electrodes. The electrodes are preferably transparentelectrodes which are arranged on the substrates in the form of acoating. The coating is commonly applied to the substrate side orsurface which is facing the switching layer.

Preferably, the electrodes are not patterned and/or structured so thatthey are contiguous. Thus, the entire switchable area is addressed andswitched at the same time by applying an electric field. In alternativeembodiments the electrodes may be patterned to form individuallyaddressable areas which may be switched independently from other areasby applying an electric field. In this case, the electrodes arepreferably patterned such that 2 to 10 independently addressable areasare present.

As described herein the liquid-crystalline medium is generally usefuland applicable in switching layers and window elements. It isparticularly useful in scattering-type switching elements and devices.

In a preferred embodiment the LC medium as used according to theinvention has a positive dielectric anisotropy. In this case preferenceis given to liquid-crystalline mixtures having a dielectric anisotropyΔε in the range from 3 to 45, more preferably in the range from 5 to 30.

Δε denotes the dielectric anisotropy, wherein Δε=ε∥−ε⊥. The dielectricanisotropy Δε is determined at 20° C. and 1 kHz.

In an alternative embodiment it is however also possible to provide anLC medium having a negative dielectric anisotropy. In this casepreference is given to liquid-crystalline mixtures having a dielectricanisotropy Δε in the range from −6 to −3.

It is particularly preferred that the medium as used according to theinvention contains, based on the overall contents of the medium, atleast 15% by weight of one or more mesogenic compounds of formula I

-   -   wherein    -   R¹ and R² denote, independently of one another, a group selected        from F, Cl, CF₃, OCF₃, and straight-chain or branched alkyl or        alkoxy having 1 to 15 carbon atoms or straight-chain or branched        alkenyl having 2 to 15 carbon atoms which is unsubstituted,        monosubstituted by CN or CF₃ or mono- or polysubstituted by        halogen and wherein one or more CH₂ groups may be, in each case        independently of one another, replaced by —O—, —S—, —CO—, —COO—,        —OCO—, —OCOO— or —C≡C— in such a manner that oxygen atoms are        not linked directly to one another,    -   A¹¹ denotes

-   -   n denotes 0 or 1, and    -   A²¹, A³¹ and A⁴¹ denote, independently of one another,

-   -   wherein L is on each occurrence, identically or differently,        halogen selected from F, Cl and Br.

Favourably the medium according to the invention can have a suitablyhigh optical anisotropy Δn, which is also known as the birefringence.The medium as described herein and as used in the switching layer andthe window element according to the invention preferably exhibits anoptical anisotropy Δn, determined at 20° C. and 589 nm, of 0.13 or more,more preferably of 0.16 or more and even more preferably of 0.20 ormore.

Above and below, Δn denotes the optical anisotropy, whereinΔn=n_(e)−n_(o), and the optical anisotropy Δn is determined at 20° C.and a wavelength of 589.3 nm.

In addition to a suitably high optical anisotropy, the medium accordingto the invention can advantageously exhibit a favourably high voltageholding ratio (VHR) in combination with good light stability and asuitably high clearing point.

Using reactive mesogens, in particular at the low amounts as specified,and preferably using chiral dopant having a high HTP, which can allowthe use in low concentrations, can advantageously contribute tomaintaining a favourably high clearing point.

The medium is a cholesteric or chiral nematic medium. Cholesteric liquidcrystals (CLCs) usually contain a medium which has, for example, in theinitial state a planar structure which reflects light having a certainwavelength, and which can be switched into a focal conic,light-scattering structure by application of an electricalalternating-voltage pulse, or vice versa. On application of a strongervoltage, in particular a stronger voltage pulse, the CLC medium can beswitched into a homeotropic, transparent state, from which it relaxesinto the planar state after rapid switching-off of the voltage or intothe focal conic state after slow switching-off.

In the planar texture Bragg reflection occurs, where the reflected lighthas the same handedness as the cholesteric helix.

In the focal conic state, the helical axes are randomly arranged and thetexture shows light scattering because of the discontinuous spatialvariations of the refractive indices at the domain boundaries.

Both planar and focal conic configurations are typically stable in theabsence of an external electric field. The effect ofelectric-field-driven textural transitions between planar and focalconic states forms the basis of operation of CLC displays, wherein whenthe texture of the CLC is switched from the planar to the focal conictexture, the Bragg reflection disappears and the CLC scatters theincident light due to the helical axes being randomly distributed

However, the switching between the states is typically achieved onlythrough the homeotropic state, where the cholesteric helix is completelyunwound by a dielectric coupling between LC molecules with positivedielectric anisotropy (Δε>0) and a vertical electric field.

In an embodiment according to the invention the scattering state of theswitching layer can be the focal conic state described above.

Alternatively, and according to a preferred embodiment, in the presentinvention the scattering state is formed by a polydomain structure.Preferably this polydomain structure can produce sufficiently strongscattering, while at the same time Bragg-type reflection behaviour stillremains observable, at least to some extent. In this phase whichcomprises, preferably consists of, polydomains the orientation of thehelical axis typically varies from domain to domain, and domainboundaries typically occur. Macroscopically however the phase can appearhomogeneous, in particular homogeneously opaque or hazy to the humaneye, and be free from visible defects over the entire layer area.

The polydomain structure is obtainable, for example, using conventionalorientation layers oriented in a planar or homeotropic manner andadvantageously switching to the polydomain state may be achievable at acomparatively low voltage. The polydomain structure is however alsoobtainable when orientation layers are not present.

In addition, the presence of the polymeric component in the modulationmaterial and the switching layer can favourably influence and stabilizethe scattering performance.

In a preferred embodiment the non-scattering or clear state can beformed by the homeotropic state described above. Using this clear statemay for example be favourable when an element with a large area is used.In this respect the advantageously high VHR that is presently obtainablecan be useful in stabilizing the element in this state againstself-discharging behaviour and thus allowing to sustain the state evenwith significantly lower refresh rates and/or lower power consumption.

Alternatively, the non-scattering or clear state can be formed by theplanar texture described above.

Using the chiral nematic or cholesteric medium can be beneficial in thatrelatively stable states, and even bistability, can be provided suchthat devices comprising the medium may consume less energy. Inparticular, a respective state may be retained, at least for aconsiderable time, after the electric field has been switched off, andless frequent addressing or refreshing of voltage may be possible.

In a preferred embodiment the window element is switchable into anoptically transparent state by applying an AC voltage V1 and isswitchable into a scattering state by applying an AC voltage V2, whereinV1>V2.

In an embodiment the switched clear state, in particular a state havinga homeotropic alignment, is maintained by applying a voltage in therange of 15 V to 100 V, more preferably 20 V to 80 V, and in particular25 V to 50 V, while the switched privacy or scattering state may bestable, at least for some time, even at 0 V.

Preferably the window element according to the invention does not usedual frequency addressing, which can simplify the required electronics.

As described above, the medium preferably exhibits a selectivereflection with a wavelength of greater than 780 nm. Accordingly themedium preferably reflects in the near infrared (NIR) spectral region.

Chiral dopants and their concentrations can be provided such that thecholesteric pitch of the medium is suitably set or adjusted. A CLCmedium can be prepared, for example, by doping a nematic LC medium witha chiral dopant having a high twisting power. The pitch p of the inducedcholesteric helix is then given by the concentration c and the helicaltwisting power HTP of the chiral dopant in accordance with equation (1):p=(HTPc)⁻¹  (1)

It is also possible to use two or more dopants, for example in order tocompensate for the temperature dependence of the HTP of the individualdopants and thus to achieve small temperature dependence of the helixpitch and the reflection wavelength of the CLC medium. For the total HTP(HTP_(total)) then approximately equation (2) holds:HTP_(total)=Σ_(i) c _(i)HTP_(i)  (2)wherein c_(i) is the concentration of each individual dopant and HTP_(i)is the helical twisting power of each individual dopant.

The liquid-crystalline medium contains one or more chiral dopants. Thechiral dopants preferably have a high absolute value of the HTP and cangenerally be added in relatively low concentrations to mesogenic basemixtures and have good solubility in the achiral component. If two ormore chiral compounds are employed, they may have the same or oppositedirection of rotation and the same or opposite temperature dependence ofthe twist.

Preferably, the one or more chiral compounds according to the inventionhave an absolute value of the helical twisting power of 5 μm⁻¹ or more,more preferably of 10 μm⁻¹ or more and even more preferably of 15 μm⁻¹or more, preferably in the commercial liquid-crystal mixture MLC-6828from Merck KGaA. Particular preference is given to chiral compoundshaving an absolute value of the helical twisting power (HTP) of 20 μm⁻¹or more, more preferably of 40 μm⁻¹ or more, even more preferably of 60μm⁻¹ or more, and most preferably in the range of 80 μm⁻¹ or more to 260μm⁻¹ or less, preferably in the commercial liquid-crystal mixtureMLC-6828 from Merck KGaA.

Preferably the one or more chiral compounds are contained in theliquid-crystalline medium in an amount, based on the overall contents ofthe medium, of 2% by weight or less, more preferably 1% by weight orless.

In a preferred embodiment of the present invention, the chiral componentconsists of two or more chiral compounds which all have the same sign ofthe HTP. The temperature dependence of the HTP of the individualcompounds may be high or low. The temperature dependence of the pitch ofthe medium can be compensated by mixing compounds having differenttemperature dependence of the HTP in corresponding ratios.

Suitable chiral dopants are known in the art, some of which arecommercially available, such as, for example, cholesteryl nonanoate,R/S-811, R/S-1011, R/S-2011, R/S-3011, R/S-4011, B(OC)2C*H—C-3 or CB15(all Merck KGaA, Darmstadt, Germany).

Particularly suitable chiral dopants are compounds which contain one ormore chiral radicals and one or more mesogenic groups, or one or morearomatic or alicyclic groups which form a mesogenic group with thechiral radical.

Suitable chiral radicals are, for example, chiral branched hydrocarbonradicals, chiral ethanediols, binaphthols or dioxolanes, furthermoremono- or polyvalent chiral radicals selected from the group consistingof sugar derivatives, sugar alcohols, sugar acids, lactic acids, chiralsubstituted glycols, steroid derivatives, terpene derivatives, aminoacids or sequences of a few, preferably 1-5, amino acids.

Preferred chiral radicals are sugar derivatives, such as glucose,mannose, galactose, fructose, arabinose and dextrose; sugar alcohols,such as, for example, sorbitol, mannitol, iditol, galactitol or anhydroderivatives thereof, in particular dianhydrohexitols, such asdianhydrosorbide (1,4:3,6-dianhydro-D-sorbide, isosorbide),dianhydromannitol (isosorbitol) or dianhydroiditol (isoiditol); sugaracids, such as, for example, gluconic acid, gulonic acid and ketogulonicacid; chiral substituted glycol radicals, such as, for example, mono- oroligoethylene or propylene glycols, wherein one or more CH₂ groups aresubstituted by alkyl or alkoxy; amino acids, such as, for example,alanine, valine, phenylglycine or phenylalanine, or sequences of from 2to 5 of these amino acids; steroid derivatives, such as, for example,cholesteryl or cholic acid radicals; terpene derivatives, such as, forexample, menthyl, neomenthyl, campheyl, pineyl, terpineyl,isolongifolyl, fenchyl, carreyl, myrthenyl, nopyl, geraniyl, linaloyl,neryl, citronellyl or dihydrocitronellyl.

Suitable chiral radicals and mesogenic chiral compounds are described,for example, in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779and DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820.

Preferable chiral compounds used according to the present invention areselected from the following groups of compounds.

In an embodiment preference is given to dopants selected from the groupconsisting of compounds of the following formulae A-I to A-III:

in which

-   -   R^(a11) and R^(a12), independently of one another, are alkyl,        oxaalkyl or alkenyl having from 2 to 9, preferably up to 7,        carbon atoms, and R^(a11) is alternatively methyl or alkoxy        having from 1 to 9 carbon atoms, preferably both are alkyl,        preferably n-alkyl,    -   R^(a21) and R^(a22), independently of one another, are alkyl or        alkoxy having from 1 to 9, preferably up to 7, carbon atoms,        oxaalkyl, alkenyl or alkenyloxy having from 2 to 9, preferably        up to 7, carbon atoms, preferably both are alkyl, preferably        n-alkyl,    -   R^(a31) and R^(a32), independently of one another, are alkyl,        oxaalkyl or alkenyl having from 2 to 9, preferably up to 7,        carbon atoms, and R^(a11) is alternatively methyl or alkoxy        having from 1 to 9 carbon atoms, preferably both are alkyl,        preferably n-alkyl.

Particular preference is given to chiral dopants selected from the groupconsisting of the compounds of the following formulae:

Further preferred dopants are derivatives of isosorbide, isomannitol orisoiditol of the following formula A-IV

in which the group

-   -   preferably dianhydrosorbitol,    -   and chiral ethanediols, such as, for example, diphenylethanediol        (hydrobenzoin), in particular mesogenic hydrobenzoin derivatives        of the following formula A-V

-   -   including the (R,S), (S,R), (R,R) and (S,S) enantiomers, which        are not shown,    -   in which

-   -   -   are each, independently of one another, 1,4-phenylene, which            may also be mono-, di- or trisubstituted by L, or            1,4-cyclohexylene,

    -   L is H, F, Cl, CN or optionally halogenated alkyl, alkoxy,        alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy having 1-7        carbon atoms,

    -   c is 0 or 1,

    -   Z⁰ is —COO—, —OCO—, —CH₂CH₂— or a single bond, and

    -   R⁰ is alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or        alkylcarbonyloxy having 1-12 carbon atoms.

Compounds of formula A-IV are described in WO 98/00428. Compounds of theformula A-V are described in GB-A-2,328,207.

In another embodiment particularly preferred chiral dopants are chiralbinaphthyl derivatives, as described in WO 02/94805, chiral binaphtholacetal derivatives, as described in WO 02/34739, chiral TADDOLderivatives, as described in WO 02/06265, and chiral dopants having atleast one fluorinated bridging group and a terminal or central chiralgroup, as described in WO 02/06196 and WO 02/06195.

Particular preference is given to chiral compounds of formula A-VI

in which

-   -   X¹, X², Y¹ and Y² are each, independently of one another, F, Cl,        Br, I, CN, SON, SF₅, straight-chain or branched alkyl having        from 1 to 25 carbon atoms, which may be monosubstituted or        polysubstituted by F, Cl, Br, I or CN and in which, in addition,        one or more non-adjacent CH₂ groups may each, independently of        one another, be replaced by —O—, —S—, —NH—, NR⁰—, —CO—, —COO—,        —OCO—, —OCOO—, —S—CO—, —CO—S—, —CH═CH— or —C≡C— in such a way        that O and/or S atoms are not bonded directly to one another, a        polymerisable group or cycloalkyl or aryl having up to 20 carbon        atoms, which may optionally be monosubstituted or        polysubstituted by halogen, preferably F, or by a polymerisable        group,    -   x¹ and x² are each, independently of one another, 0, 1 or 2,    -   y¹ and y² are each, independently of one another, 0, 1, 2, 3 or        4,    -   B¹ and B² are each, independently of one another, an aromatic or        partially or fully saturated aliphatic six-membered ring in        which one or more CH groups may be replaced by N atoms and one        or more non-adjacent CH₂ groups may be replaced by O and/or S,    -   W¹ and W² are each, independently of one another,        —Z¹-A¹-(Z²-A²)_(m)-R, and one of the two is alternatively R¹ or        A³, but both are not simultaneously H, or

-   -   U¹ and U² are each, independently of one another, CH₂, O, S, CO        or CS,    -   V¹ and V² are each, independently of one another, (CH₂)_(n), in        which from one to four non-adjacent CH₂ groups may be replaced        by 0 and/or S, and one of V¹ and V² and, in the case where

both are a single bond,

-   -   Z¹ and Z² are each, independently of one another, —O—, —S—,        —CO—, —COO—, —OCO—, —O—COO—, —CO—NR⁰—, —NR⁰—CO—, —O—CH₂—,        —CH₂—O—, —S—CH₂—, —CH₂—S—, —CF₂—O—, —O—CF₂—, —OF₂—S—, —S—CF₂—,        —CH₂—CH₂—, —CF₂—CH₂—, —CH₂—CF₂—, —CF₂—CF₂—, —CH═N—, —N═CH—,        —N═N—, —CH═CH—, —CF═CH—, —CH═CF—, —CF═CF—, —C≡C—, a combination        of two of these groups, where no two O and/or S and/or N atoms        are bonded directly to one another, preferably —CH═CH—COO—, or        —COO—CH═CH—, or a single bond,    -   A¹, A² and A³ are each, independently of one another,        1,4-phenylene, in which one or two non-adjacent CH groups may be        replaced by N, 1,4-cyclohexylene, in which one or two        non-adjacent CH₂ groups may be replaced by 0 and/or S,        1,3-dioxolane-4,5-diyl, 1,4-cyclohexenylene,        1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,        naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl or        1,2,3,4-tetrahydronaphthalene-2,6-diyl, where each of these        groups may be monosubstituted or polysubstituted by L, and in        addition A¹ is a single bond,    -   L is a halogen atom, preferably F, CN, NO₂, alkyl, alkoxy,        alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy having 1-7        carbon atoms, in which one or more H atoms may be replaced by F        or Cl,    -   m is in each case, independently, 0, 1, 2 or 3, and    -   R and R¹ are each, independently of one another, H, F, Cl, Br,        I, CN, SCN, SF₅, straight-chain or branched alkyl having from 1        or 3 to 25 carbon atoms respectively, which may optionally be        monosubstituted or polysubstituted by F, Cl, Br, I or CN, and in        which one or more non-adjacent CH₂ groups may be replaced by        —O—, —S—, —NH—, —NR⁰—, —CO—, —COO—, —OCO—, —O—COO—, —S—CO—,        —CO—S—, —CH═CH— or —C≡C—, where no two 0 and/or S atoms are        bonded directly to one another, or a polymerisable group.

Particular preference is given to chiral binaphthyl derivatives of theformula A-VI-1

in particular those selected from the following formulae A-VI-1a toA-VI-1c:

-   -   in which B and Z⁰ are as defined for formula A-IV, and Z⁰ more        preferably is —OCO— or a single bond,    -   R⁰ is as defined for formula A-IV or H or alkyl having from 1 to        4 carbon atoms, and    -   b is 0, 1 or 2.

Particular preference is furthermore given to chiral binaphthylderivatives of the formula A-VI-2

in particular to those selected from the following formulae A-VI-2a toA-VI-2f:

in which R⁰ is as defined for formula A-VI, and X is H, F, Cl, CN or R⁰,preferably F.

In a particularly preferred embodiment, the chiral medium according tothe invention comprises one or more compounds of formula R-5011 andS-5011 which are shown in Table F below. In an embodiment the mediumcontains R-5011. In another embodiment the medium contains S-5011.

The LC medium according to the present invention preferably andfavourably exhibits a high reliability and a high electric resistivity.The LC medium according to the present invention also preferably andfavourably exhibits a high voltage holding ratio (VHR), see S. Matsumotoet al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SIDConference, San Francisco, June 1984, p. 304 (1984); T. Jacob and U.Finkenzeller in “Merck Liquid Crystals—Physical Properties of LiquidCrystals”, 1997. The VHR of an LC medium according to the invention ispreferably 85%, more preferably ≥90%, even more preferably ≥95% andparticularly preferably ≥98%. Unless described otherwise, themeasurement of the VHR is carried out as described in T. Jacob, U.Finkenzeller in “Merck Liquid Crystals—Physical Properties of LiquidCrystals”, 1997.

According to the invention the medium comprises one or morepolymerisable mesogenic compounds in an amount, based on the overallcontents of the medium, of 5% by weight or less.

Preferably, the one or more polymerisable mesogenic compounds arecontained in the medium in an amount, based on the overall contents ofthe medium, in an amount of 3.5% by weight or less, even more preferablyin an amount of 2.5% by weight or less and particularly preferably in anamount of 1.25% by weight or less.

Preferably, one or more of the one or more polymerisable mesogeniccompounds comprise one, two or more acrylate and/or methacrylate groups.

In the medium according to the invention preferably one or morepolymerisable, curable or hardenable compounds are provided, preferablyone or more photocurable monomers, which can favourably serve as theprecursors for the polymeric component in the modulation material andthe switching layer.

The reactive mesogens (RMs) or mesogenic monomers used contain amesogenic group and one or more polymerisable groups, i.e. functionalgroups which are suitable for polymerisation.

In a particularly preferred embodiment the polymerisable compound(s)used include(s) only reactive mesogen(s), i.e. all the reactive monomersare mesogens. Alternatively, RMs can be provided in combination with oneor more non-mesogenic polymerisable compounds. The RMs can bemonoreactive and/or di- or multireactive.

In a preferred embodiment of the invention one or more of the one ormore polymerisable mesogenic compounds are selected from the compoundsof the formula MR^(Ma)-A^(M1)-(Z^(M1)-A^(M2))_(m1)-R^(Mb)  Min which the individual radicals are defined as follows:

-   -   R^(Ma) and R^(Mb) are each independently P, P-Sp-, H, F, Cl, Br,        I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN, SF₅ or straight-chain or        branched alkyl having 1 to 25 carbon atoms, in which one or more        non-adjacent CH₂ groups may each independently also be replaced        by —C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰⁰)—, —O—, —S—, —CO—, —CO—O—,        —O—CO—, —O—CO—O—, in such a way that no oxygen and/or sulphur        atoms are joined directly to one another, and in which one or        more hydrogen atoms may also be replaced by F, Cl, Br, I, CN, P        or P-Sp-, where preferably at least one of the R^(Ma) and R^(Mb)        radicals is or contains a P or P-Sp- group,    -   preferably    -   R^(Ma) and R^(Mb) are each independently P, P-Sp-, H, halogen,        SF₅, NO₂, an alkyl, alkenyl or alkynyl group, where preferably        at least one of the R^(Ma) and R^(Mb) radicals is or contains a        P or P-Sp- group,    -   P is a polymerisable group,    -   Sp is a spacer group or a single bond,    -   A^(M1) and A^(M2) are each independently an aromatic,        heteroaromatic, alicyclic or heterocyclic group, preferably        having 4 to 25 ring atoms, preferably carbon atoms, which also        comprises or may contain fused rings, and which may optionally        be mono- or polysubstituted by L,    -   L is P, P-Sp-, OH, CH₂OH, F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS,        —OCN, —SCN, —C(═O)N(R^(x))₂, —C(═O)Y¹, —C(═O)R^(x), —N(R^(x))₂,        optionally substituted silyl, optionally substituted aryl having        6 to 20 carbon atoms, or straight-chain or branched alkyl,        alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or        alkoxycarbonyloxy having 1 to 25 carbon atoms or alkenyl or        alkynyl having 2 to 25 carbon atoms, in which one or more        hydrogen atoms may also be replaced by F, Cl, P or P-Sp-,        preferably P, P-Sp-, H, OH, CH₂OH, halogen, SF₅, NO₂, an alkyl,        alkenyl or alkynyl group,    -   Y¹ is halogen, preferably F,    -   Z^(M1) is —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH₂—,        —CH₂O—, —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —OF₂S—, —SCF₂—,        —(CH₂)_(n1)—, —CF₂CH₂—, —CH₂CF₂—, —(CF₂)_(n1)—, —CH═CH—,        —CF═CF—, —C≡C—, —CH═CH—, —COO—, —OCO—CH═CH—, CR⁰R⁰⁰ or a single        bond,    -   R⁰ and R⁰⁰ are each independently H or alkyl having 1 to 12        carbon atoms,    -   R^(x) is P, P-Sp-, H, halogen, straight-chain, branched or        cyclic alkyl having 1 to 25 carbon atoms, in which one or more        non-adjacent CH₂ groups may also be replaced by —O—, —S—, —CO—,        —CO—O—, —O—CO—, —O—CO—O—, in such a way that no oxygen and/or        sulphur atoms are joined directly to one another, and in which        one or more hydrogen atoms may also be replaced by F, Cl, P or        P-Sp-, an optionally substituted aryl or aryloxy group having 6        to 40 carbon atoms, or an optionally substituted heteroaryl or        heteroaryloxy group having 2 to 40 carbon atoms,    -   m1 is 0, 1, 2, 3 or 4, and    -   n1 is 1, 2, 3 or 4,    -   where at least one substituent, preferably one, two or three        substituents and more preferably one or two substituents from        the group of R^(Ma), R^(Mb) and the substituent L present is a P        or P-Sp- group or contains at least one P or P-Sp- group.

Particular preference is given to compounds of the formula M in whichone of R^(ma) and R^(mb) or both are P or P-Sp-.

Suitable and preferred RMs for use in the liquid crystalline mediaaccording to the invention are, for example, selected from the followingformulae:

in which the individual radicals are defined as follows:

-   -   P¹ to P³ are each independently a polymerisable group,        preferably having one of the definitions specified above and        below for P, more preferably an acrylate, methacrylate,        fluoroacrylate, oxetane, vinyloxy or epoxy group,    -   Sp¹ to Sp³ are each independently a single bond or a spacer        group, preferably having one of the definitions of Sp given        above and below, and more preferably —(CH₂)_(p1)—,        —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or —(CH₂)_(p1)—O—CO—O—, in        which p1 is an integer from 1 to 12, and where the bond to the        adjacent ring in the latter groups is via the oxygen atom, where        one of the P¹-Sp¹-, P²-Sp²- and P³-Sp³- radicals may also be        R^(aa),    -   R^(aa) is H, F, Cl, CN or straight-chain or branched alkyl        having 1 to 25 carbon atoms, in which one or more non-adjacent        CH₂ groups may each independently also be replaced by        C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,        —O—CO—O—, in such a way that no oxygen and/or sulphur atoms are        joined directly to one another, and in which one or more        hydrogen atoms may also be replaced by F, Cl, CN or P¹-Sp¹-,        more preferably straight-chain or branched, optionally mono- or        polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,        alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms        (where the alkenyl and alkynyl radicals have at least two and        the branched radicals at least three carbon atoms),    -   R⁰ and R⁰⁰ are the same or different at each instance and are        each independently H or alkyl having 1 to 12 carbon atoms,    -   R^(y) and R^(z) are each independently H, F, CH₃ or CF₃,    -   Z¹ is —O—, —CO—, —C(R^(y)R^(z))— or —CF₂CF₂—,    -   Z² and Z³ are each independently —CO—O—, —O—CO—, —CH₂O—, —OCH₂—,        —CF₂O—, —OCF₂— or —(CH₂)_(n)—, where n is 2, 3 or 4,    -   L is the same or different at each instance and has the meaning        given under formula M above, preferably is F, Cl, CN, or        straight-chain or branched, optionally mono- or polyfluorinated        alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl        or alkylcarbonyloxy having 1 to 12 carbon atoms, preferably F,    -   L′ and L″ are each independently H, F or Cl,    -   X¹ to X³ are independently of one another —CO—O—, —O—CO— or a        single bond,    -   r is 0, 1, 2, 3 or 4,    -   s is 0, 1, 2 or 3,    -   t is 0, 1 or 2, and    -   x is 0 or 1.

Suitable polymerisable compounds are listed, for example, in Table G.Particularly preferred reactive mesogens are compounds of formulae RM-ARM-B, RM-C, RM-D, RM-E, RM-F and RM-G as shown respectively in Examples1, 2, 3 and 5.

The polymerisable compounds have at least one polymerisable group. Thepolymerisable group is preferably selected from CH₂═CW¹—COO—,

CH₂═CW²—(O)_(k1)—, CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—,(CH₂═CH)₂CH—O—, (CH₂═CH—CH₂)₂N—, HO—CW²W³—, HS—CW²W³—, HW²N—,HO—CW²W³—NH—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—,Phe-CH═CH—, HOOC—, OCN—, with W¹ being H, Cl, CN, phenyl or alkyl with 1to 5 C atoms, in particular H, Cl or CH₃, W² and W³ being independentlyof each other H or alkyl with 1 to 5 C atoms, in particular H, methyl,ethyl or n-propyl, Phe being 1,4-phenylene and k₁ and k₂ beingindependently of each other 0 or 1. The polymerisable or reactive groupis preferably selected from a vinyl group, an acrylate group, amethacrylate group, a fluoroacrylate group, an oxetane group or an epoxygroup, especially preferably an acrylate group or a methacrylate group.

In an embodiment, non-mesogenic monomers are included in the medium inaddition to the one or more RMs. Preferably, one or more polymerisablecompounds, either the non-mesogenic monomers or the RMs or both, areselected from acrylates, methacrylates, fluoroacrylates and vinylacetate, wherein the composition more preferably further comprises oneor more direactive and/or trireactive polymerisable compounds,preferably selected from diacrylates, dimethacrylates, triacrylates andtrimethacrylates.

In a preferred embodiment the medium according to the inventioncomprises one or more non-mesogenic monoacrylates, particularlypreferably one or more compounds selected from methyl acrylate, ethylacrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, t-butylacrylate, pentyl acrylate, hexyl acrylate, nonyl acrylate, 2-ethylhexylacrylate, 2-hydroxyethyl acrylate, 2-hydroxy-butyl acrylate andisobornyl acrylate.

Additionally or alternatively the medium according to the inventionpreferably comprises one or more non-mesogenic monomethacrylates,particularly preferably one or more compounds selected from methylmethacrylate, ethyl methacrylate, propyl methacrylate, isopropylmethacrylate, butyl methacrylate, t-butyl methacrylate, pentylmethacrylate, hexyl methacrylate, nonyl methacrylate, dodecylmethacrylate, 2-ethyl-hexyl methacrylate, 2-hydroxy-ethyl methacrylate,2-hydroxy-butyl methacrylate, isobornyl methacrylate and 1-adamantylmethacrylate.

It is particularly preferred that at least one crosslinking agent isadded to the medium, i.e. a polymerisable compound containing two ormore polymerisable groups, wherein preferably di- or multireactive RMsare used.

In this respect direactive and multireactive compounds can serve to formpolymer networks of their own and/or to crosslink polymer chains formedsubstantially from polymerising monoreactive compounds.

Alternatively or additionally, conventional crosslinkers known in theart can be used. It is particularly preferred to additionally providedireactive or multireactive acrylates and/or methacrylates. Particularlypreferred compounds are selected from ethylene diacrylate, propylenediacrylate, butylene diacrylate, pentylene diacrylate, hexylenediacrylate, glycol diacrylate, glycerol diacrylate, pentaerythritoltetraacrylate, ethylene dimethacrylate, also known as ethyleneglycoldimethacrylate, propylene diamethcrylate, butylene dimethacrylate,pentylene dimethacrylate, hexylene dimethacrylate, tripropylene glycoldiacrylate, glycol dimethacrylate, glycerol dimethacrylate,trimethylpropane trimethacrylate and pentaerythritol triacrylate.

The ratio of monoreactive monomers and di- or multireactive monomers canbe favourably set and adjusted to influence the properties of thepolymeric component to be formed.

Suitable and conventionally used thermal initiators or photoinitiatorscan be added to the medium to facilitate the reaction, for example azocompounds or organic peroxides such as Luperox type initiators.Moreover, suitable conditions for the polymerisation and suitable typesand amounts of initiators are known in the art and are described in theliterature. In case a polymerisation initiator is included in themedium, the use of a photoinitiator is preferred.

For example, when polymerising by means of UV light, a photoinitiatorcan be used that decomposes under UV irradiation to produce freeradicals or ions that start the polymerisation reaction. Forpolymerising acrylate or methacrylate groups preferably a radicalphotoinitiator is used. For polymerising vinyl, epoxide or oxetanegroups preferably a cationic photoinitiator is used. It is also possibleto use a thermal polymerisation initiator that decomposes when heated toproduce free radicals or ions that start the polymerisation. Typicalradical photoinitiators are for example the commercially availableIrgacure®, e.g. Irgacure 651 (available from BASF, containing2,2-dimethoxy-1,2-diphenyl ethan-1-one), or Darocure® (Ciba Geigy AG,Basel, Switzerland). A typical cationic photoinitiator is for exampleUVI 6974 (Union Carbide). Further useful photoiniators includeα-aminoketones, e.g. Irgacure 907, coumarins, phosphine oxides, e.g.Irgacure 2100, acyl phosphines, e.g. Irgacure 819.

In a particular embodiment the added polymerisation initiator,preferably photoinitiator, comprises, preferably consists of, one ormore mesogenic polymerisation initiators, preferably one or moremesogenic photoinitiators, i.e. one or more reactive compounds which caninitiate polymerisation and which themselves have anisotropic andmesogenic properties.

However, according to a particularly preferred embodiment nopolymerisation initiator, in particular no photoinitiator, is used. Incertain cases this may improve the VHR and reduce the tendency toproduce ions in the switching layer.

In order to maintain and achieve a good VHR, preferably impurities inthe reaction products of the polymerisation are kept at a minimum or aresubstantially avoided. In particular, residual reactive species andcharged contaminants are suitably and preferably kept at a minimum. Forexample, in case UV polymerisation is carried out, in a preferredembodiment light with a comparatively long wavelength which isapproaching the visible spectrum is used, preferably UV light in therange from 340 nm to 380 nm, and even more preferably from 360 nm to 380nm is advantageously used. This way unwanted photodegradation ordecomposition of components of the LC medium may be avoided or at leastminimized. In case a photoinitiator is used, the irradiation wavelengthand the photoinitiator can be suitably matched or adjusted.

In an alternative case where no photoinitiator is used, which in someembodiments is preferable, the wavelength range may be set such that atleast some of the polymerisable compounds can undergo a photoreactionand initiate the polymerisation reaction by themselves, whilefurthermore degradation or decomposition of non-reactive components ofthe LC medium may be avoided or at least minimized. Obtaining andsetting of the desired wavelength range can be achieved by conventionalmethods known in the art, e.g. by using optical filters, in particularedge filters.

It has surprisingly been found that the medium according to theinvention can be favourably used to produce polymeric structures in situby providing the one or more polymerisable mesogenic compounds as setforth above and below in the medium.

The polymerisable compounds in the medium may be chosen such that afterthe polymerisation a stable system is obtained, which e.g. can be stablein further processing steps such as thermal heating steps, wherein agood VHR may be maintained.

Furthermore, according to the invention only a relatively small amountof (a) polymerisable mesogenic compound(s) is used which can favourablyinfluence the stability and minimized unwanted degradation.

According to the invention the medium is used to prepare a modulationmaterial which comprises a polymeric component, in particular apolymeric network, wherein the polymeric component is obtained by orrespectively obtainable from polymerising the polymerisable compound(s)as set forth above and below.

The provision of the polymeric component may be useful in stabilizingone or more states or phases of the LC medium.

Preferably, the polymeric component is contained in the medium in anamount, based on the overall contents of the medium, in the range from0.1% by weight to 5% by weight, more preferably in the range from 0.5%by weight to 1.5% by weight.

The polymeric component can contribute to the advantageous properties ofthe obtainable material. For example, the polymeric component maycontribute to a significantly more stable scattering state, inparticular the polydomain state, such that this scattering state may bemaintained for more extended periods of time, in particular up to days,without refreshing or reapplying voltage.

Furthermore, the polymeric component as provided in the material whichcontains the CLC medium according to the invention can favourablyinfluence the scattering efficiency and appearance, e.g. in terms ofuniformity and viewing angle dependence. Thereby colour effects whichmay arise under oblique viewing angles can be significantly reduced.

In a preferred embodiment the modulation material comprises theliquid-crystalline medium and the polymeric component, where thepolymeric component comprises a polymer network which is obtained bypolymerisation of reactive mesogens, where the reactive mesogenspreferably contain at least one group selected from acrylate groups,particularly preferably from monoacrylate groups, diacrylate groups ortriacrylate groups, vinyl ether groups and epoxide groups. Compoundscontaining acrylate group(s) as used herein comprise acrylic monomers,methacrylic monomers, and mixtures of such monomers.

Polymerisation can be carried out using conventional methods. Thepolymerisation can be carried out in one or more steps. In particular,polymerisation of the polymerisable compound(s) is preferably achievedby exposure to heat or to actinic radiation, wherein exposure to actinicradiation means irradiation with light, like UV light, visible light orIR light, irradiation with X-rays or gamma rays, or irradiation withhigh-energy particles, such as ions or electrons. In a preferredembodiment free radical polymerisation is carried out.

Polymerisation can be carried out at a suitable temperature. In anembodiment polymerisation is performed at a temperature below theclearing point of the mesogenic mixture. In an alternative embodiment itis however also possible to carry out the polymerisation at or above theclearing point.

In an embodiment, polymerisation is carried out by photoirradiation,i.e. with light, preferably UV light. As a source for actinic radiation,for example a single UV lamp or a set of UV lamps can be used. Whenusing a high lamp power the curing time can be reduced. Another possiblesource for photoradiation is a laser, like e.g. a UV laser, a visiblelaser or an IR laser.

In an embodiment, polymerisation is carried out by adding to the chiralliquid crystalline host mixture one or more polymerisable compounds,preferably comprising a di-reactive compound and optionally a suitablephotoinitiator, and polymerising the polymerisable compounds by exposureto UV irradiation.

Preferably the polymerisation is carried out in electro-optical cellsmaintained in a pre-determined state of the chiral liquid crystallinehost mixture. In a preferred embodiment polymerisation, preferablypolymerisation using UV light, is carried out when the medium is in thehomeotropic state, wherein typically and preferably an electric field isapplied.

The medium may contain additional compounds such as one or morepleochroic dyes, in particular one or more dichroic dyes, and/or othercustomary and suitable additives, preferably in an amount from 0.01% byweight to 25% by weight, more preferably from 0.1% by weight to 5% byweight.

Pleochroic dyes preferably are dichroic dyes and can be selected fromfor example azo dyes, anthraquinones, methine compounds, azomethinecompounds, merocyanine compounds, naphthoquinones, tetrazines,pyrromethene dyes, malononitrile dyes, rylenes, in particular perylenesand terylenes, thiadiazole dyes, thienothiadiazole dyes,benzothiadiazoles, pyrromethenes and diketopyrrolopyrroles. Particularpreference is given to azo compounds, anthraquinones, benzothiadiazoles,in particular as described in WO 2014/187529, diketopyrrolopyrroles, inparticular as described in WO 2015/090497, and rylenes, in particular asdescribed in WO 2014/090373.

However, preferably the switching layer does not comprise any dyes,which can provide higher transmission in the clear state and give anuncoloured or respectively white appearance.

It is particularly preferred that the window element, more preferablythe window including the window element according to the inventioncontains only one switching layer.

In an alternative embodiment it is however also possible to provide morethan one switching layer, in particular two switching layers, in thewindow element, for example two layers which both provide switchablescattering modes or one layer providing switchable scattering andanother layer providing switchable dimming of light.

In a particular embodiment the switching layer according to theinvention is combined with another switching layer which comprises aguest-host LC medium in a window element to control and regulate thepassage of light. The respective switching layers may be suitablyseparated by using for example one or more interjacent substrates orsheets, panes or panels, wherein optionally panes may be furtherseparated by a vacuum or a gas filled space.

According to the invention the present liquid-crystalline mediumcontains the one or more compounds of formula I as set forth above andbelow in an amount, based on the overall contents of the medium, of atleast 15% by weight, preferably at least 20% by weight, more preferablyat least 25% by weight, even more preferably at least 30% by weight andin particular at least 35% by weight.

In an embodiment the one or more compounds of formula I are contained inthe medium in an amount, based on the overall contents of the medium, inthe range from 15% by weight to 75% by weight, more preferably from 20%by weight to 65% by weight, even more preferably from 20% by weight to55% by weight and in particular from 25% by weight to 50% by weight.

The medium according to the invention thus comprises at least onecompound of formula I. In many cases it can however be beneficial andpreferred that two, three or more compounds of formula I are containedin the medium.

Preferably the group A¹¹ as defined in formula I denotes

In another embodiment n as defined in formula I denotes 0.

In a preferred embodiment the one or more compounds of formula I areselected from compounds of formulae Ia, Ib and Ic, more preferably fromcompounds of formulae Ia and Ib

wherein

-   -   R¹ and R² denote, independently of one another, a group selected        from F, Cl, CF₃, OCF₃, and straight-chain or branched alkyl or        alkoxy having 1 to 15 carbon atoms or straight-chain or branched        alkenyl having 2 to 15 carbon atoms which is unsubstituted,        monosubstituted by CN or CF₃ or mono- or polysubstituted by        halogen and wherein one or more CH₂ groups may be, in each case        independently of one another, replaced by —O—, —S—, —CO—, —COO—,        —OCO—, —OCOO— or —C≡C— in such a manner that oxygen atoms are        not linked directly to one another, preferably from F, CF₃,        OCF₃, straight-chain alkyl or alkoxy having 1 to 9 carbon atoms        or alkenyl having 2 to 9 carbon atoms, and    -   L is on each occurrence, identically or differently, H or        halogen selected from F, Cl and Br, preferably from F and Cl,        and more preferably is on each occurrence, identically or        differently, H or F.

It is particularly preferred that in case the phenylene rings of thecompounds of formula I are substituted that the substituent(s) is (are)F, and furthermore that the terminal groups R¹ and R² do not contain Cl.

In a preferred embodiment the amount of Cl-containing compounds includedin the medium is limited, preferably is limited to 55% by weight orless, based on the overall contents of the medium, more preferably to40% by weight or less, and even more preferably to 25% by weight orless. In a particularly preferred embodiment the liquid-crystallinemedium contains no Cl-containing compounds.

Accordingly it is also preferred to limit the amount of Cl-containingcompounds in the component of the LC medium which consists of thecompounds of formula I as set forth above and below, preferably to 55%by weight or less, based on the overall contents of compounds of formulaI which are comprised in the medium, more preferably to 40% by weight orless, and even more preferably to 25% by weight or less. In aparticularly preferred embodiment the one or more compounds of formula Iare selected from compounds which do not contain Cl.

It is furthermore particularly preferred that at least one of the ringsA²¹, A³¹ and A⁴¹ according to formula I has at least one F substituent.It is furthermore particularly preferred that the rings A²¹, A³¹ and A⁴¹according to formula I together have at least two F substituents.

In the medium according to the invention the use of compounds containingCN is preferably and favourably limited, preferably to 75% by weight orbelow, more preferably to 50% by weight or below, even more preferablyto 25% by weight or below and in particular to 15% by weight or below,and in a particularly preferred embodiment is completely avoided.

In addition to the one or more compounds of formula I theliquid-crystalline medium according to the invention preferably containsone or more further mesogenic compounds. It is preferred that theseadditional compounds are also added in view of contributing to ormaintaining the favourable properties of the medium, e.g. a good VHR anda favourable stability.

In an embodiment the liquid-crystalline medium according to theinvention further comprises one or more compounds of formula II

wherein

-   -   R³ and R⁴ denote, independently of one another, a group selected        from F, CF₃, OCF₃, CN, and straight-chain or branched alkyl or        alkoxy having 1 to 15 carbon atoms or straight-chain or branched        alkenyl having 2 to 15 carbon atoms which is unsubstituted,        monosubstituted by CN or CF₃ or mono- or polysubstituted by        halogen and wherein one or more CH₂ groups may be, in each case        independently of one another, replaced by —O—, —S—, —CO—, —COO—,        —OCO—, —OCOO— or —C≡C— in such a manner that oxygen atoms are        not linked directly to one another, preferably from F, CF₃,        OCF₃, CN, straight-chain alkyl or alkoxy having 1 to 9 carbon        atoms or alkenyl having 2 to 9 carbon atoms,    -   and    -   L¹, L² and L³ denote, independently of one another, H or F.

In a further embodiment the liquid-crystalline medium according to theinvention further comprises one or more compounds of formula III

wherein R⁵ and R⁶ are defined as R³ and L⁴ and L⁵ are defined as L¹ forformula II above.

Therefore, it is preferred that the medium contains, based on theoverall contents of the medium, at least 15% by weight of one or moremesogenic compounds of formula I, optionally one or morephotoinitiators, and one or more mesogenic compounds selected from thegroup of compounds of formulae II and III.

It is particularly preferred that the medium comprises one or morecompounds of formula I, one or more compounds of formula II and one ormore compounds of formula III as set forth above.

Preferably the liquid-crystalline medium according to the inventionfurther comprises one or more compounds of formula IV

wherein

-   -   R⁷ denotes straight-chain or branched alkyl or alkoxy having 1        to 15 carbon atoms, preferably 1 to 7 carbon atoms, or        straight-chain or branched alkenyl having 2 to 15 carbon atoms        which is unsubstituted, monosubstituted by CN or CF₃ or mono- or        polysubstituted by halogen and wherein one or more CH₂ groups        may be, in each case independently of one another, replaced by        —O—, —S—, —CO—, —COO—, —OCO—, —OCOO— or —C≡C— in such a manner        that oxygen atoms are not linked directly to one another,    -   i is 0, 1 or 2,    -   L⁶ and L⁷ are, independently of one another, H or F, and    -   X¹ denotes F, CF₃, OCF₃ or CN.

Compounds of formula II preferably are used in the medium in a totalconcentration from 1% by weight to 45% by weight, more preferably from5% by weight to 25% by weight.

Compounds of formula III preferably are used in the medium in a totalconcentration from 1% by weight to 45% by weight, more preferably from5% by weight to 25% by weight.

Compounds of formula IV preferably are used in the medium in a totalconcentration from 1% by weight to 45% by weight, more preferably from5% by weight to 25% by weight.

It is particularly preferred that the medium comprises one or morecompounds of formula I as set forth above and below, one or morecompounds of formula II, one or more compounds of formula III and one ormore compounds of formula IV.

In a particularly preferred embodiment one or more of the one or morecompounds of formula I are selected from compounds of formulae I-1 andI-2

-   -   wherein    -   R¹ and R² are as defined for formula Ia above, and    -   L is on each occurrence, identically or differently, H or F.

Optionally the media according to the present invention may comprisefurther liquid crystal compounds in order to adjust the physicalproperties. Such compounds are known in the field. The concentration ofthese optionally further included liquid crystal compounds in the mediaaccording to the present invention is preferably from 0% by weight to30% by weight, more preferably from 0.1% by weight to 20% by weight andmost preferably from 1% by weight to 15% by weight.

Preferably the medium according to the present invention comprises oneor more compounds of

-   -   PGP-n-m, PGP-n-mV, PGU-n-F, PGIGI-n-F, GGP-n-F, GGP-n-Cl, in        particular GGP-5-Cl, CPGP-n-m, CPGP-n-OT, CPGU-n-OT, DPGU-n-F,        and/or    -   CPP-n-m, CPG-n-F, CGU-n-F, BCH.n.F.F.F., in particular        BCH.7.F.F.F, and/or    -   CP-n-m, CP-n-N, and/or    -   a compound of formula R-5011 or S-5011, and/or    -   one or more reactive polymerisable compounds, and/or    -   one or more polymerisation initiators,        wherein the meanings and structures of the respective        abbreviations or acronyms are explained and illustrated in the        Tables below.

The liquid-crystalline media according to the present invention maycontain further additives in usual concentrations. The totalconcentration of these further constituents is in the range of 0% to10%, preferably 0.1% to 6%, based on the total mixture. Theconcentrations of the individual compounds used each are preferably inthe range of 0.01% to 3%. The concentration of these and of similaradditives is herein not taken into consideration for the values andranges of the concentrations of the liquid crystal components andcompounds of the liquid crystal media. This also holds for theconcentration of dichroic dyes optionally used in the mixtures, whichare not counted when the concentrations of the compounds respectivelythe components of the host mixture are specified. The concentration ofthe respective additives is always given relative to the final dopedmixture.

Herein, unless explicitly stated otherwise, all concentrations are givenin weight percent.

The liquid-crystalline media according to the present invention consistof several compounds, preferably of 3 to 30, more preferably of 4 to 20,and most preferably of 4 to 16 compounds. These compounds are mixed in aconventional way. As a rule, the required amount of the compound used inthe smaller amount is dissolved in the compound used in the greateramount. In case the temperature is above the clearing point of thecompound used in the higher concentration, it is particularly easy toobserve completion of the process of dissolution. It is, however, alsopossible to prepare the media by other conventional ways, e.g. using socalled pre-mixtures, which can be e.g. homologous or eutectic mixturesof compounds or using so called multi-bottle systems, the constituentsof which are ready to use mixtures themselves.

Many of the mesogenic compounds or mixtures thereof described above andbelow are commercially available. These compounds are either known orcan be prepared by methods which are known per se, as described in theliterature (for example in the standard works such as Houben-Weyl,Methoden der Organischen Chemie [Methods of Organic Chemistry],Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditionswhich are known and suitable for said reactions. Use may also be madehere of variants which are known per se, but are not mentioned here ingreater detail. The media according to the invention are prepared in amanner conventional per se. In general, the components are dissolved inone another, preferably at elevated temperature. Suitable additives orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the alignment of the liquid-crystalline phases.

The medium may further comprise customary additives such as stabilizers,antioxidants, free radical scavengers, chain transfer agents, e.g.thioethers, and/or plasticizers.

Stabilizers may be useful to further stabilize the modulation materialagainst degradation or oxidation, e.g. due to thermal stress or UVradiation.

In a further aspect of the invention there is provided aliquid-crystalline medium which comprises a compound having the formula

It was presently recognized that advantageous liquid-crystalline media,which are especially suitable as host media for the presently describedscattering applications, can be obtained by including this compoundwhich is designated as BCH-7F.F.F. It is particularly preferred thatthis compound is included in the medium as set forth above and below.

Preferably, the host medium as described above, but also the chiralnematic medium according to the invention, comprises in addition toBCH-7F.F.F a compound having the formula

It is furthermore preferred that the medium contains one or morecompounds selected from the compounds designated as PCH-n as shown inTable D, in particular selected from PCH-3 and PCH-5.

The term “alkyl” according to the present invention preferablyencompasses straight-chain and branched alkyl groups having 1 to 7carbon atoms, particularly the straight-chain groups methyl, ethyl,propyl, butyl, pentyl, hexyl and heptyl. Groups having 2 to 5 carbonatoms are generally preferred.

An alkoxy can be straight-chain or branched, and it preferably isstraight-chain and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms, andaccordingly is preferably methoxy, ethoxy, propoxy, butoxy, pentoxy,hexoxy or heptoxy.

The term “alkenyl” according to the present invention preferablyencompasses straight-chain and branched alkenyl groups having 2-7 carbonatoms, in particular the straight-chain groups. Particularly preferredalkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl, C₅-C₇-4E-alkenyl,C₆-C₇-5E-alkenyl and C₇-6E-alkenyl, in particular C₂-C₇-1E-alkenyl,C₄-C₇-3E-alkenyl and C₅-C₇-4E-alkenyl. Examples of preferred alkenylgroups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl,1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl,4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl and6-heptenyl. Groups having up to 5 carbon atoms are generally preferred.

Fluorinated alkyl or alkoxy preferably comprises CF₃, OCF₃, CFH₂, OCFH₂,CF₂H, OCF₂H, C₂F₅, OC₂F₅, CFHCF₃, CFHCF₂H, CFHCFH₂, CH₂CF₃, CH₂CF₂H,CH₂CFH₂, CF₂CF₂H, CF₂CFH₂, OCFHCF₃, OCFHCF₂H, OCFHCFH₂, OCH₂CF₃,OCH₂CF₂H, OCH₂CFH₂, OCF₂CF₂H, OCF₂CFH₂, C₃F₇ or OC₃F₇, in particularCF₃, OCF₃, CF₂H, OCF₂H, C₂F₅, OC₂F₅, CFHCF₃, CFHCF₂H, CFHCFH₂, CF₂CF₂H,CF₂CFH₂, OCFHCF₃, OCFHCF₂H, OCFHCFH₂, OCF₂CF₂H, OCF₂CFH₂, C₃F₇ or OC₃F₇,particularly preferably OCF₃ or OCF₂H. Fluoroalkyl in a preferredembodiment encompasses straight-chain groups with terminal fluorine,i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl,5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions offluorine are not precluded, however.

Oxaalkyl preferably encompasses straight-chain groups of the formulaC_(n)H_(2n+1)—O—(CH₂)_(m), where n and m are each, independently of oneanother, from 1 to 6. Preferably, n=1 and m is 1 to 6.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl),2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl,2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl,or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

Halogen is preferably F or Cl, in particular F.

If one of the above mentioned groups is an alkyl group in which one CH₂group has been replaced by —CH═CH—, this can be straight-chain orbranched. It is preferably straight-chain and has 2 to 10 carbon atoms.Accordingly, it is in particular vinyl, prop-1- or prop-2-enyl, but-1-,-2- or but-3-enyl, pent-1-, -2-, -3- or pent-4-enyl, hex-1-, -2-, -3-,-4- or hex-5-enyl, hept-1-, -2-, -3-, -4-, -5- or hept-6-enyl, oct-1-,-2-, -3-, -4-, -5-, -6- or oct-7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-,-7- or non-8-enyl, dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- ordec-9-enyl.

If one of the above mentioned groups is an alkyl group in which one CH₂group has been replaced by —O— and one has been replaced by —CO—, theseare preferably adjacent. These thus contain an acyloxy group —CO—O— oran oxycarbonyl group —O—CO—. These are preferably straight-chain andhave 2 to 6 carbon atoms.

They are accordingly in particular acetyloxy, propionyloxy, butyryloxy,pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl,butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl,2-propionyloxy-ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl,3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonyl-methyl, propoxycarbonylmethyl, butoxycarbonylmethyl,2-(meth-oxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxy-carbonyl)butyl.

If one of the above mentioned groups is an alkyl group in which one CH₂group has been replaced by unsubstituted or substituted —CH═CH— and anadjacent CH₂ group has been replaced by CO, CO—O or O—CO, this can bestraight-chain or branched. It is preferably straight-chain and has 4 to13 carbon atoms. Accordingly, it is in particular acryloyloxymethyl,2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl,5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl,8-acryloyloxy-octyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl,methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl,4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or9-methacryloyloxynonyl.

If one of the above mentioned groups is an alkyl or alkenyl group whichis monosubstituted by CN or CF₃, this group is preferablystraight-chain. The substitution by CN or CF₃ is in any position.

If one of the above mentioned groups is an alkyl or alkenyl group whichis at least monosubstituted by halogen, this group is preferablystraight-chain and halogen is preferably F or Cl, more preferably F. Inthe case of polysubstitution, halogen is preferably F. The resultinggroups also include perfluorinated groups. In the case ofmonosubstitution, the fluoro or chloro substituent can be in any desiredposition, but is preferably in the ω-position.

Compounds containing branched groups may occasionally be of importanceowing to better solubility in some conventional liquid-crystalline basematerials. However, they are particularly suitable as chiral dopants ifthey are optically active.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched groups are isopropyl, 2-butyl(=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy,1-methylhexoxy or 1-methylheptoxy.

If one of the above mentioned groups is an alkyl group in which two ormore CH₂ groups have been replaced by —O— and/or —CO—O—, this can bestraight-chain or branched. It is preferably branched and has 3 to 12carbon atoms. Accordingly, it is in particular biscarboxymethyl,2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl,5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl,8,8-biscarboxyoctyl, 9,9-bis-carboxynonyl, 10,10-biscarboxydecyl,bis(methoxycarbonyl)methyl, 2,2-bis-(methoxycarbonyl)ethyl,3,3-bis(methoxycarbonyl)propyl, 4,4-bis(methoxy-carbonyl)butyl,5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)-hexyl,7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl,bis-(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl,3,3-bis(ethoxy-carbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl or5,5-bis(ethoxycarbonyl)-pentyl.

In another aspect of the invention a switching layer is provided whichcomprises the medium or the modulation material according to theinvention.

The switching layer according to the invention preferably has athickness in the range from 1 μm to 100 μm, more preferably from 2 μm to50 μm, even more preferably from 4 μm to 40 μm and in particular from 10μm to 25 μm.

It is also possible to provide two or more layers in combination, forexample in a window element, where the layers are separated bysubstrates or suitable sheets, panes or panels.

According to the invention a switching element and in particular awindow element comprising the switching layer can be provided, whereinthe switching layer is arranged between two substrates, in particulartwo transparent substrates.

The substrates may comprise, preferably consist of, glass or a polymer,in particular glass, polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polyvinylbutyral (PVB), polymethyl methacrylate(PMMA), polycarbonate (PC), polyimide (PI), COP (cyclic olefin polymers)or TAC (triacetylcellulose).

In a particularly preferred embodiment glass substrates are used.

The window element can influence the passage of light, in particular byelectrically switching the switching layer between an opticallytransparent or clear state and a scattering state.

The window element according to the invention or the window in which thewindow element can be integrated preferably comprises one or more layerswhich block UV light. In particular, the window element preferablycomprises one or more layers which do not allow, or only do so to a verysmall proportion, the passage of light having a wavelength of less than350 nm, preferably extending to less than 360 nm, particularlypreferably even extending to less than 380 nm.

The window element can be useful in several window applications, e.g.for providing privacy or anti-glare. The window element may for examplebe arranged as a switchable glazing unit. It may be incorporated in aninsulated glazing unit.

Advantageously the window element can be produced by the facile andefficient process described herein.

In the preparation method the liquid-crystalline medium which comprisesthe one or more polymerisable mesogenic compounds is provided as a layerbetween two opposing transparent substrates which are each provided withan electrode. Preferably the electrodes are arranged as conductivelayers above the inner surface of each substrate, wherein morepreferably the conductive layers are respectively arranged on apassivation layer, even more preferably arranged between passivationlayers, and wherein optionally alignment layers are further providedwhich are in direct contact with the liquid-crystalline medium.

Subsequently the one or more polymerisable mesogenic compounds arepolymerised, in particular in the presence of an applied electric fieldin the layer.

It is preferred that polymerising is carried out by photopolymerisation,preferably using UV light. In a particularly preferred embodiment duringthe polymerisation, at least temporarily, an electric field is appliedto induce an alignment of the medium, preferably a homeotropicalignment.

The application of a voltage to set a predetermined orientation duringpolymerisation can favourably influence the product properties of theswitching layer and the window element. For example, inducing ahomeotropic alignment during polymerisation can contribute to achievinga homogeneous low haze clear state, while furthermore a homogeneous andsuitably strong haze can be obtained in the scattering state.

It is possible to control the temperature during photopolymerisation,for example in a range from 20° C. to 100° C., preferably below theclearing point.

In an embodiment the reactive mesogens are self-starting, while inanother embodiment a photoinitiator is used to trigger thepolymerisation.

For the photopolymerisation of the material in the switching layerpreferably an exposure time from 30 s to 240 min, more preferably from 1min to 120 min is used, preferably using irradiation intensities in therange from 0.01 mW/cm² to 100 mW/cm² to, more preferably from 0.1 mW/cm²to 50 mW/cm² and in particular from 1 mW/cm² to 20 mW/cm².

For the polymerisation several parameters may be suitably set or varied,e.g. the irradiation dose, the applied voltage, the frequency of the ACvoltage, and the amount of chiral dopant in the medium.

Following the polymerisation, in particular the photopolymerisation stepfurther treatments may be carried out. Preferably a thermal treatment iscarried out after the polymerisation step, either in the presence orabsence of an electric field. The thermal treatment, i.e. an exposure toan increased temperature relative to the previous polymerisation stepmay lead to further curing or further conversion rate or completion ofthe polymerisation.

It is also possible to perform pretreatment steps on the substratesused, for example surface treatment methods such as a UV-ozone treatmentor a plasma treatment, which can improve alignment and wetting behaviourover larger areas and contribute to an improved homogeneity as well as afavourable reduction of unwanted haze in the clear state.

The method described herein is advantageously useful to produce a windowelement with favourable durability, colour neutrality, a low haze clearstate and a scattering state giving good privacy, even in the case whereonly a single switching layer is used in the device.

In the present invention and especially in the following Examples, thestructures of the mesogenic compounds are indicated by means ofabbreviations, also called acronyms. In these acronyms, the chemicalformulae are abbreviated as follows using Tables A to C below. Allgroups C_(n)H_(2n+1), C_(m)H_(2m+1) and C_(l)H_(2l+1) or C_(n)H_(2n−1),C_(m)H_(2m−1) and C_(l)H_(2l−1) denote straight-chain alkyl or alkenyl,preferably 1-E-alkenyl, each having n, m and l C atoms respectively.Table A lists the codes used for the ring elements of the corestructures of the compounds, while Table B shows the linking groups.Table C gives the meanings of the codes for the left-hand or right-handend groups. The acronyms are composed of the codes for the ring elementswith optional linking groups, followed by a first hyphen and the codesfor the left-hand end group, and a second hyphen and the codes for theright-hand end group. Table D shows illustrative structures of compoundstogether with their respective abbreviations.

TABLE A Ring elements

C

P

D

DI

A

AI

G

GI

U

UI

Y

M

MI

N

NI

Np

dH

N3f

N3fl

tH

tHI

tH2f

tH2fl

K

KI

L

LI

F

FI

Nf

Nfl

TABLE B Linking groups E —CH₂CH₂— Z —CO—O— V —CH═CH— ZI —O—CO— X —CF═CH—O —CH₂—O— XI —CH═CF— OI —O—CH₂— B —CF═CF— Q —CF₂—O— T —C≡C— QI —O—CF₂— W—CF₂CF₂—

TABLE C End groups Left-hand side Right-hand side Used alone -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO— C_(n)H_(2n+1)—O— —On—O—C_(n)H_(2n+1) —V— CH₂═CH— —V —CH═CH₂ -nV— C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ —Vn- CH₂═CH—C_(n)H_(2n+1)— —Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) —N— N≡C— —N —C≡N —S— S═C═N— —S —N═C═S—F— F— —F —F —Cl— Cl— —Cl —Cl —M— CFH₂— —M —CFH₂ —D— CF₂H— —D —CF₂H —T—CF₃— —T —CF₃ —MO— CFH₂O— —OM —OCFH₂ —DO— CF₂HO— —OD —OCF₂H —TO— CF₃O——OT —OCF₃ —FXO— CF₂═CH—O— —OXF —O—CH═CF₂ —A— H—C≡C— —A —C≡C—H -nA—C_(n)H_(2n+1)—C≡C— —An —C≡C—C_(n)H_(2n+1) —NA— N≡C—C≡C— —AN —C≡C—C≡NUsed together with one another and with others —. . .A. . .— —C≡C— —. ..A. . . —C≡C— —. . .V. . .— CH═CH— —. . .V. . . —CH═CH— —. . .Z. . .——CO—O— —. . .Z. . . —CO—O— —. . .ZI. . .— —O—CO— —. . .ZI. . . —O—CO— —.. .K. . .— —CO— —. . .K. . . —CO— —. . .W. . .— —CF═CF— —. . .W. . .—CF═CF— wherein n and m each denote integers, and the three dots “. . .”are place-holders for other abbreviations from this table.

The following table shows illustrative structures together with theirrespective abbreviations. These are shown in order to illustrate themeaning of the rules for the abbreviations. They furthermore representcompounds which may be preferably used.

TABLE D Illustrative structures

wherein n, m and l preferably, independently of one another, denote 1 to7.

The following table shows illustrative compounds which can be used asstabilizers in the media according to the present invention.

TABLE E

Table E shows possible stabilizers which can be added to the LC mediaaccording to the invention, wherein n denotes an integer from 1 to 12,preferably 1, 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are notshown.

The LC media preferably comprise 0 to 10% by weight, in particular 1 ppmto 5% by weight, particularly preferably 1 ppm to 1% by weight, ofstabilizers.

Table F below shows illustrative compounds which can preferably be usedas chiral dopants in the mesogenic media according to the presentinvention.

TABLE F

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the compounds shown inTable F.

The mesogenic media according to the present invention preferablycomprise two or more, preferably four or more, compounds selected fromthe compounds shown in the above tables D to F.

In an embodiment the LC media according to the present inventionpreferably comprise three or more, more preferably five or morecompounds shown in Table D.

TABLE G

RM-1

RM-2

RM-3

RM-4

RM-5

RM-6

RM-7

RM-8

RM-9

RM-10

RM-11

RM-12

RM-13

RM-14

RM-15

RM-16

RM-17

RM-18

RM-19

RM-20

RM-21

RM-22

RM-23

RM-24

RM-25

RM-26

RM-27

RM-28

RM-29

RM-30

RM-31

RM-32

RM-33

RM-34

RM-35

RM-36

RM-37

RM-38

RM-39

RM-40

RM-41

RM-42

RM-43

RM-44

RM-45

RM-46

RM-47

RM-48

RM-49

RM-50

RM-51

RM-52

RM-53

RM-54

RM-55

RM-56

RM-57

RM-58

RM-59

RM-60

RM-61

RM-62

RM-63

RM-64

RM-65

RM-66

RM-67

RM-68

RM-69

RM-70

RM-71

RM-72

RM -73

RM-74

RM-75

RM-76

RM-77

RM-78

RM-79

RM-80

RM-81

RM-82

RM-83

RM-84

RM-85

RM-86

RM-87

RM-88

RM-89

RM-90

RM-91

RM-92

RM-93

RM-94

RM-95

RM-96

RM-97

RM-98

RM-99

RM-100

RM-101

RM-102

RM-103

RM-104

RM-105

RM-106

RM-107

RM-108

RM-109

RM-110

RM-111

RM-112

RM-113

RM-114

RM-115

RM-116

RM-117

RM-118

RM-119

RM-120

RM-121

Table G collates example compounds which can be used in the LC mediaaccording to the present invention, preferably as reactive mesogeniccompounds. Preferably an initiator or a mixture of two or moreinitiators is added for the polymerisation. The initiator or initiatormixture is preferably added in amounts of 0.001% to 2% by weight, basedon the mixture. A suitable initiator is, for example, Irgacure®651 (fromBASF).

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table G.

The liquid crystalline media according to the present invention comprisepreferably four or more, more preferably six or more, even morepreferably seven or more, and particularly preferably eight or morecompounds selected from the group of compounds of table D, preferablycompounds of three or more different formulae selected from the group offormulae of table D. It is particularly preferred that the mediumadditionally contains one, two or more compounds selected from the groupof formulae of table E. Even more preferably the medium further containsone, two or more compounds selected from the group of formulae of tableG.

The following examples are merely illustrative of the present inventionand they should not be considered as limiting the scope of the inventionin any way. The examples and modifications or other equivalents thereofwill become apparent to those skilled in the art in the light of thepresent disclosure.

However, the physical properties and compositions shown in the followingillustrate which properties can be achieved and in which ranges they canbe modified. Especially the combination of the various properties, whichcan be preferably achieved, is thus well defined.

EXAMPLES

Liquid crystal mixtures and composite systems are realized with thecompositions and properties as given in the following. Their propertiesand optical performance are investigated.

Reference Example 1

A liquid-crystal base mixture B-1 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

GGP-5-Cl  17.00% Clearing point: 101.0° C. PGIGI-3-F  7.00% Δn [589 nm,20° C.]: 0.181 CPG-2-F  8.00% n_(e) [589 nm, 20° C.]: 1.693 CPG-3-F 8.00% Δϵ [1 kHz, 20° C.]: 13.2 CPG-5-F  5.00% ϵ_(∥) [1 kHz, 20° C.]:18.0 CGU-2-F  7.00% CGU-3-F  7.00% CGU-5-F  4.00% PGU-2-F  8.00% PGU-3-F 8.00% CPGU-3-F  10.00% CPP-3-2  5.00% CGPC-3-3  3.00% CGPC-5-3  3.00% Σ100.00%

Reference Example 2

A liquid-crystal base mixture B-2 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PP-1-2V1  8.00% Clearing point: 98.0° C. CP-3-O1  7.00% Δn [589 nm,20° C.]: 0.231 CP-3-Cl  3.00% n_(e) [589 nm, 20° C.]: 1.755 PGP-2-2V 9.00% Δε [1 kHz, 20° C.]: 7.0 PGP-3-2V  6.00% ε_(∥) [1 kHz, 20° C.]:11.0 PGU-3-F  4.00% GGP-3-Cl  9.00% GGP-5-Cl  20.00% GPEP-2-Cl  8.00%GPEP-5-Cl  12.00% PGIGI-3-F  5.00% CPGP-4-3  3.00% CPGP-5-2  3.00%DPGU-4-F  3.00% Σ 100.00%

Reference Example 3

A liquid-crystal base mixture B-3 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGIGI-3-F  12.00% Clearing point: 104.0° C. CPG-2-F  8.00% Δn [589 nm,20° C.]: 0.161 CPG-3-F  8.00% Δε [1 kHz, 20° C.]: 10.9 CPG-5-F  5.00%ε_(∥) [1 kHz, 20° C.]: 15.2 CPU-5-F  10.00% CPU-7-F  10.00% PGU-3-F 4.00% PGU-5-F  9.00% CCGU-3-F  8.00% CPP-3-2  4.00% CGPC-3-3  3.00%CGPC-5-3  3.00% CGPC-5-5  3.00% CPGU-3-OT  3.00% CP-5-N  10.00% Σ100.00%

Reference Example 4

A liquid-crystal base mixture B-4 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGIGI-3-F  10.00% Clearing point: 105.0° C. CPG-2-F  6.00% Δn [589 nm,20° C.]: 0.160 CPG-3-F  7.00% n_(e) [589 nm, 20° C.]: 1.663 CPG-5-F 5.00% Δε [1 kHz, 20° C.]: 10.0 CPU-5-F  10.00% CPU-7-F  10.00% PGU-3-F 4.00% PGU-5-F  7.00% CCGU-3-F  8.00% CPP-3-2  4.00% CGPC-3-3  3.00%CGPC-5-3  3.00% CGPC-5-5  3.00% CPGU-3-OT  5.00% CP-5-N  15.00% Σ100.00%

Reference Example 5

A liquid-crystal base mixture B-5 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  CP-5-N  15.00% Clearing point: 101.0° C PGIGI-3-F  10.00% Δn [589 nm,20° C.]: 0.173 CPG-2-F  6.00% n_(e) [589 nm, 20° C.]: 1.680 CPG-3-F 7.00% Δε [1 kHz, 20° C.]: 11.0 CPG-5-F  5.00% ε_(∥) [1 kHz, 20° C.]:15.2 CPU-5-F  10.00% CPU-7-F  10.00% PGU-3-F  4.00% PGU-5-F  3.00%PGP-2-3  4.00% PGP-2-4  5.00% PGP-2-5  4.00% CCGU-3-F  8.00% CPGP-3-OT 5.00% CPGP-5-2  4.00% Σ 100.00%

Reference Example 6

A liquid-crystal base mixture B-6 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  APUQU-3-F  8.00% Clearing point: 127.8° C. CPU-3-F  15.00% Δn [589 nm,20° C.]: 0.206 CCGU-3-F  8.00% n_(e) [589 nm, 20° C.]: 1.711 CPGP-5-2 4.00% Δε [1 kHz, 20° C.]: 42.7 CPGP-5-3  4.00% ε_(∥) [1 kHz, 20° C.]:48.2 CPGU-3-OT  8.00% DPGU-4-F  4.00% PGU-2-F  10.00% PGU-3-F  11.00%PGUQU-3-F  8.00% PGUQU-4-F  10.00% PGUQU-5-F  10.00% Σ 100.00%

Reference Example 7

A liquid-crystal base mixture B-7 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  CP-3-N  14.00% Clearing point: 119.3° C. PTP-1-O2  8.00% Δn [589 nm,20° C.]: 0.236 PTP-3-O1  6.00% n_(e) [589 nm, 20° C.]: 1.752 CP-3-O1 8.50% Δε [1 kHz, 20° C.]: 7.2 PGP-2-2V  8.00% ε_(∥) [1 kHz, 20° C.]:11.0 CPGP-4-3  5.00% CPGP-5-2  5.00% PGP-2-3  5.00% PGP-2-4  5.00%PGP-2-5  10.00% CPTP-3-O1  6.00% CPTP-3-O2  6.00% PGUQU-3-F  7.50%PGUQU-4-F  2.00% PP-1-2V1  4.00% Σ 100.00%

Reference Example 8

A liquid-crystal base mixture B-8 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  CP-1V-N  16.00% Clearing point: 110.1° C. PP-2-N  7.00% Δn [589 nm,20° C.]: 0.218 PGUQU-3-F  10.00% n_(e) [589 nm, 20° C.]: 1.737 CPG-2-F 10.00% Δε [1 kHz, 20° C.]: 11.1 PP-1-2V1  10.00% ε_(∥) [1 kHz, 20° C.]:15.3 PGIGI-3-F  12.00% CPGP-5-2  8.00% CPGP-5-3  8.00% PGP-2-3  7.00%PGP-2-4  6.00% PGP-2-5  6.00% Σ 100.00%

Reference Example 9

A liquid-crystal base mixture B-9 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PUQU-2-F  6.00% Clearing point: 98.1° C. PUQU-3-F  12.00% Δn [589 nm,20° C.]: 0.166 PGU-2-F  5.00% n_(e) [589 nm, 20° C.]: 1.668 PGU-3-F 11.00% Δε [1 kHz, 20° C.]: 11.4 PPGU-3-F  4.00% ε_(∥) [1 kHz, 20° C.]:15.2 CPGP-5-2  7.00% CPGP-5-3  6.00% CPGP-4-3  7.00% CC-3-V  25.00%PGP-2-3  4.00% PGP-2-4  4.00% CPU-3-F  9.00% Σ 100.00%

Reference Example 10

A liquid-crystal base mixture B-10 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGUQU-3-F  6.00% Clearing point: 101.0° C. PGUQU-4-F  10.00% Δn [589nm, 20° C.]: 0.194 PGUCU-5-F  10.00% n_(e) [589 nm, 20° C.]: 1.699PUQU-3-F  17.00% Δε [1 kHz, 20° C.]: 37.0 PGU-2-F  10.00% ε_(∥) [1 kHz,20° C.]: 42.9 PGU-3-F  11.00% CPGU-3-OT  8.00% CCGU-3-F  8.00% CPU-3-F 12.00% CPGP-5-2  4.00% CPGP-5-3  4.00% Σ 100.00%

Reference Example 11

A liquid-crystal base mixture B-11 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  CP-3-O1  8.00% Clearing point: 111.5° C. CC-3-V  12.00% Δn [589 nm,20° C.]: 0.213 CPGP-5-2  6.00% n_(e) [589 nm, 20° C.]_(:) 1.729 CPGP-5-3 6.00% Δε [1 kHz, 20° C.]: 3.1 PGP-2-2V  14.00% ε_(∥) [1 kHz, 20° C.]:6.3 PGP-1-2V  13.00% PGP-3-2V  13.00% PGP-2-5  6.00% PP-1-2V1  12.00%PUQU-3-F  6.00% PGUQU-3-F  4.00% Σ 100.00%

Reference Example 12

A liquid-crystal base mixture B-12 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGIGI-3-F  8.00% Clearing point: 102.0° C. GGP-3-F  8.00% Δn [589 nm,20° C.]: 0.169 GGP-5-F  7.00% n_(e) [589 nm, 20° C.]: 1.675 CPG-2-F 7.00% Δε [1 kHz, 20° C.]: 12.2 CPG-3-F  7.00% ε_(∥) [1 kHz, 20° C.]:16.9 CPG-5-F  5.00% CPU-5-F  10.00% PGU-3-F  4.00% PGU-5-F  7.00%CCGU-3-F  8.00% CGPC-3-3  3.00% CGPC-5-3  3.00% CGPC-5-5  3.00%CPGU-3-OT  5.00% CP-5-N  15.00% Σ 100.00%

Reference Example 13

A liquid-crystal base mixture B-13 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGIGI-3-F  7.00% Clearing point: 99.9° C. GGP-3-F  8.00% Δn [589 nm,20° C.]: 0.179 GGP-5-F  7.00% n_(e) [589 nm, 20° C.]: 1.681 CPG-3-F 7.00% Δε [1 kHz, 20° C.]: 13.9 CPG-5-F  5.00% ε_(∥) [1 kHz, 20° C.]:18.7 CPU-5-F  10.00% PGU-2-F  6.00% PGU-3-F  6.00% PGU-5-F  7.00%CCGU-3-F  8.00% CGPC-3-3  3.00% CGPC-5-3  3.00% CGPC-5-5  3.00%CPGU-3-OT  5.00% CP-5-N  15.00% Σ 100.00%

Reference Example 14

A liquid-crystal base mixture B-14 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGIGI-3-F  6.00% Clearing point: 101.0° C. GGP-3-F  7.00% Δn [589 nm,20° C.]: 0.174 GGP-5-F  8.00% n_(e) [589 nm, 20° C.]: 1.684 CPG-2-F 9.00% Δε [1 kHz, 20° C.]: 12.6 CPG-3-F  8.00% ε_(∥) [1 kHz, 20° C.]:17.4 CPG-5-F  8.00% PGU-2-F  7.00% PGU-3-F  7.00% PGU-5-F  7.00%CCGU-3-F  8.00% CGPC-3-3  4.00% CGPC-5-3  4.00% CGPC-5-5  4.00% CP-5-N 13.00% Σ 100.00%

Reference Example 15

A liquid-crystal base mixture B-15 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  CCGU-3-F  8.00% Clearing point: 105.0° C. BCH-5F.F.F  10.00% Δn [589nm, 20° C.]: 0.160 PGU-5-F  7.00% n_(e) [589 nm, 20° C.]: 1.663PGIGI-3-F  10.00% Δε [1 kHz, 20° C.]: 11.4 BCH-2F.F  6.00% ε_(∥) [1 kHz,20° C.]: 15.7 BCH-7F.F.F  10.00% BCH-3F.F  7.00% CBC-53F  3.00% BCH-5F.F 5.00% CBC-55F  3.00% BCH-32  4.00% PCH-5  15.00% PGU-3-F  4.00%CPGU-3-OT  5.00% CBC-33F  3.00% Σ 100.00%

Reference Example 16

A liquid-crystal base mixture B-16 is prepared and characterized withrespect to its general physical properties, having the composition andproperties as indicated in the following table.

  PGU-5-F  9.00% Clearing point: 92.0° C. PGIGI-3-F  7.00% Δn [589 nm,20° C.]: 0.163 BCH-2F.F  6.00% n_(e) [589 nm, 20° C.]: 1.670 PGU-2-F 9.00% BCH-3F.F  6.00% CBC-53F  3.00% BCH-5F.F  5.00% CBC-55F  3.00%BCH-32  7.00% PCH-7  14.00% PCH-5  15.00% PGU-3-F  9.00% CBC-33  4.00%CBC-33F  3.00% Σ 100.00%

Example 1

A cholesteric mixture C-1 is prepared by mixing 97.01% of mixture B-1 asdescribed in Reference Example 1 above with 0.42% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 1.25% of compoundof formula RM-A

0.62% of compound of formula RM-B

0.62% of compound of formula RM-C

and 0.08% of the photoinitiator Irgacure® 651 (abbreviated as IRG-651 inthe following)

available from Ciba, Switzerland.

The obtained pitch of mixture C-1 is 1.84 μm.

The pitch is confirmed by measuring the wavelength of the selectivereflection maximum λ_(max) at 20° C. using the NIR spectroscopic methoddescribed above.

The mixture C-1 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar, TN), wherein thecell gap is 25 μm, and the filling ports are sealed. Electrical wiringis applied to the cell by soldering.

Subsequently polymerisation is carried out by irradiating the test cellwith UV light (UVA and UVB, 3.5 mW/cm² light intensity) while asquare-wave voltage (70V, 60 Hz) is applied.

After the polymerisation the haze is determined according to ASTM1003-92 using a spectrophotometer (Lambda 1050, Perkin Elmer) and a 150mm Ulbricht's sphere.

The obtained cell has a clear state which at 63V has 6% haze and 100%clarity. Furthermore, at 0V the cell has a privacy (scattering) statewith 100% haze and 13% clarity.

Clarity herein is determined using haze-gard i from BYK-Gardner.

No undesirable off-axis colour effects are observed.

Example 2

A cholesteric mixture C-2 is prepared by mixing 98.28% of mixture B-1 asdescribed in Reference Example 1 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany, 0.63% of compound offormula RM-D

0.63% of compound of formula RM-E

and 0.04% of IRG-651.

The obtained pitch of mixture C-2 is 1.84 μm.

The mixture C-2 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar, TN), wherein thecell gap is 20 μm, and the filling ports are sealed. Electrical wiringis applied to the cell by soldering.

The filled test cell is further treated and measured as described inExample 1.

The obtained cell after polymerisation has a clear state which at 50Vhas 4% haze and 100% clarity. Furthermore, at 0V the cell has a privacy(scattering) state with 100% haze and 18% clarity.

No undesirable off-axis colour effects are observed.

Comparative Example 1

A cholesteric mixture CC-1 is prepared by mixing 99.58% of mixture B-1as described in Reference Example 1 above with 0.42% of chiral dopantR-5011 available from Merck KGaA, Darmstadt.

The mixture CC-1 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar, TN), wherein thecell gap is 35 μm, and the filling ports are sealed. Electrical wiringis applied to the cell by soldering.

The obtained cell has a clear state which at 63V has 3% haze and 100%clarity. Furthermore, at 3V the cell has a privacy (scattering) statewith 79% haze and 25% clarity.

The cell exhibits an undesirable colour effect resembling a rainbow-likeappearance with angular dependence when observed off-axis.

Comparative Example 2

A cholesteric mixture CC-2 is prepared by mixing 98.70% of mixture B-1as described in Reference Example 1 above with 0.63% of compound offormula RM-D as shown in Example 2 above, 0.63% of compound of formulaRM-E as shown in Example 2 above and 0.04% of IRG 651.

The mixture CC-2 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar alignment), whereinthe cell gap is 25 μm, and the filling ports are sealed. Electricalwiring is applied to the cell by soldering.

The filled test cell is further treated and measured as described inExample 1.

The obtained cell after polymerisation has a privacy (scattering) statewhich at 70V has 54% haze. However, the cell exhibits no clear state,where at 3V the haze is still 21%.

Example 3

A cholesteric mixture C-3 is prepared by mixing 98.28% of mixture B-1 asdescribed in Reference Example 1 above with 0.42% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 0.63% of compoundof formula RM-D as shown in Example 2 above, 0.58% of compound offormula RM-E as shown in Example 2 above, 0.05% of compound of formulaRM-F

and 0.04% of IRG 651.

The mixture C-3 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar alignment), whereinthe cell gap is 25 μm, and the filling ports are sealed. Electricalwiring is applied to the cell by soldering.

The filled test cell is further treated as described in Example 1.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Example 4

A cholesteric mixture C-4 is prepared by mixing 98.64% of mixture B-1 asdescribed in Reference Example 1 above with 0.42% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 0.45% of compoundof formula RM-D as shown in Example 2 above, 0.45% of compound offormula RM-E as shown in Example 2 above and 0.04% of IRG 651.

The mixture C-4 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar alignment), whereinthe cell gap is 20 μm, and the filling ports are sealed. Electricalwiring is applied to the cell by soldering.

The filled test cell is further treated as described in Example 1.

The obtained cell after polymerisation has a clear state which at 50Vhas 3% haze and 100% clarity. Furthermore, at 0V the cell has a privacy(scattering) state with 100% haze and 10% clarity.

No undesirable off-axis colour effects are observed.

Example 5

A cholesteric mixture C-5 is prepared by mixing 98.58% of mixture B-1 asdescribed in Reference Example 1 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany and 1.00% of compound offormula RM-G

The mixture C-5 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (vertical alignment), wherein the cell gap is 20 μm, and thefilling ports are sealed. Electrical wiring is applied to the cell bysoldering.

The filled test cell is further treated and measured as described inExample 1.

The obtained cell after polymerisation has a clear state which at 50Vhas 5% haze and 100% clarity. Furthermore, at 0V the cell has a privacy(scattering) state with 100% haze and 15% clarity.

No undesirable off-axis colour effects are observed.

Example 6

A cholesteric mixture C-6 is prepared by mixing 98.61% of mixture B-1 asdescribed in Reference Example 1 with 0.64% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany and 0.75% of compound offormula RM-G as shown in Example 5 above.

The mixture C-6 is filled by vacuum filling into a test cell havingglass substrates with ITO electrodes as well as polyimide alignmentlayers (AL-1054 from Japan Synthetic Rubber, planar, TN), wherein thecell gap is 15 μm, and the filling ports are sealed. Electrical wiringis applied to the cell by soldering.

Subsequently polymerisation is carried out by irradiating the test cellwith UV light (UVA and UVB, 3.5 mW/cm² light intensity) while asquare-wave voltage (50V, 60 Hz) is applied.

The obtained cell after polymerisation has a clear state which at 50Vhas 2% haze and 100% clarity. Furthermore, at 0V the cell has a privacy(scattering) state with 100% haze and 35% clarity.

No undesirable off-axis colour effects are observed.

Example 7

A cholesteric mixture C-7 is prepared by mixing 98.28% of mixture B-12as described in Reference Example 12 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany, 0.63% of compound offormula RM-D as shown in Example 2 above, 0.63% of compound of formulaRM-E as shown in Example 2 above and 0.04% of IRG-651.

The obtained pitch of mixture C-7 is 1.84 μm.

The mixture C-7 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 25 μm.

Subsequently polymerisation is carried out by irradiating the test cellwith UV light (UVACUBE 2000, Hönle, 9 mW/cm² light intensity) for 10minutes while a square-wave voltage (70V, 60 Hz) is applied.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 94.4% is obtained. In the clear state ahaze value of 2.3% is obtained.

Example 8

A cholesteric mixture C-8 is prepared by mixing 98.28% of mixture B-4 asdescribed in Reference Example 4 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany, 0.63% of compound offormula RM-D as shown in Example 2 above, 0.63% of compound of formulaRM-E as shown in Example 2 above and 0.04% of IRG-651.

The obtained pitch of mixture C-8 is 1.84 μm.

The mixture C-8 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 25 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 95.7% is obtained. In the clear state ahaze value of 2.6% is obtained.

Example 9

A cholesteric mixture C-9 is prepared by mixing 98.28% of mixture B-14as described in Reference Example 14 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany, 0.63% of compound offormula RM-D as shown in Example 2 above, 0.63% of compound of formulaRM-E as shown in Example 2 above and 0.04% of IRG-651.

The obtained pitch of mixture C-9 is 1.84 μm.

The mixture C-9 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 25 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 96.7% is obtained. In the clear state ahaze value of 3.3% is obtained.

Example 10

A cholesteric mixture C-10 is prepared by mixing 98.28% of mixture B-13as described in Reference Example 13 with 0.42% of chiral dopant R-5011available from Merck KGaA, Darmstadt, Germany, 0.63% of compound offormula RM-D as shown in Example 2 above, 0.63% of compound of formulaRM-E as shown in Example 2 above and 0.04% of IRG-651.

The obtained pitch of mixture C-10 is 1.84 μm.

The mixture C-10 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 25 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 96.7% is obtained. In the clear state ahaze value of 2.5% is obtained.

Comparative Example 3

A cholesteric mixture CC-3 is prepared by mixing 91.12% of mixture B-1as described in Reference Example 1 above with 6.49% of chiral dopant CB15 available from Merck KGaA, Darmstadt, Germany, 2.37% ofethyleneglycol dimethacrylate and 0.02% of IRG-651.

The mixture CC-3 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 25 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 95.1% is obtained. In the clear state ahaze value of 4.3% is obtained.

Example 11

A cholesteric mixture C-11 is prepared by mixing 98.61% of mixture B-4as described in Reference Example 4 above with 0.64% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, and 0.75% ofcompound of formula RM-G as shown in Example 5 above.

No photoinitiator is added. The obtained pitch of mixture C-11 is 1.1μm.

The mixture C-11 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 15 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 95% is obtained. In the clear state a hazevalue of 2.1% is obtained.

Example 12

A cholesteric mixture C-12 is prepared by mixing 98.68% of mixture B-4as described in Reference Example 4 above with 0.57% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, and 0.75% ofcompound of formula RM-G as shown in Example 5 above.

No photoinitiator is added. The obtained pitch of mixture C-12 is 1.24μm.

The mixture C-12 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 18 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined. In the scattering(hazy) state a haze value of 97% is obtained. In the clear state a hazevalue of 3.5% is obtained.

Example 13

A cholesteric mixture C-13 is prepared by mixing 98.61% of mixture B-15as described in Reference Example 15 above with 0.64% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, and 0.75% ofcompound of formula RM-G as shown in Example 5 above.

The mixture C-13 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 20 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Example 14

A cholesteric mixture C-14 is prepared by mixing 98.78% of mixture B-15as described in Reference Example 15 above with 0.44% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 0.75% of compoundof formula RM-G as shown in Example 5 above, and 0.03% of compound offormula A-1

The mixture C-14 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 20 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Example 15

A cholesteric mixture C-15 is prepared by mixing 98.75% of mixture B-15as described in Reference Example 15 above with 0.44% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 0.75% of compoundof formula RM-G as shown in Example 5 above, 0.03% of compound offormula A-1 as shown in Example 14 above, and 0.03% of compound offormula A-2

The mixture C-15 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 20 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Example 16

A cholesteric mixture C-16 is prepared by mixing 98.82% of mixture B-16as described in Reference Example 16 above with 0.40% of chiral dopantR-5011 available from Merck KGaA, Darmstadt, Germany, 0.75% of compoundof formula RM-G as shown in Example 5 above, and 0.03% of compound offormula A-1 as shown in Example 14 above.

The mixture C-16 is filled into a test cell having glass substrates withITO electrodes as well as polyimide alignment layers (AL-1054 from JapanSynthetic Rubber, planar, TN), wherein the cell gap is 20 μm.

Subsequently polymerisation is carried out as described in Example 7.

After the polymerisation the haze is determined.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Example 17

A cholesteric mixture C-17 is prepared by mixing mixture B-15 asdescribed in Reference Example 15 above with chiral dopant S-1011available from Merck KGaA, Darmstadt, Germany such that a pitch of 2 μmis obtained, wherein 99.25% of this mixture is further mixed with 0.75%of compound of formula RM-G as shown in Example 5 above to obtainmixture C-17.

The mixture C-17 is further treated as described in Example 1.

The cell exhibits favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

Examples 18 to 26

Cholesteric mixtures C-18, C-19, C-20, C-21, C-22, C-23, C-24, C-25 andC-26 are prepared and further treated according to Example 2, whereinhowever instead of the chiral dopant R-5011 the chiral dopant S-1011 isused and wherein instead of mixture B-1 respectively the mixtures B-2,B-3, B-5, B-6, B-7, B-8, B-9, B-10 and B-11 as described respectively inReference Examples 2, 3 and 5 to 11 are used.

The cells exhibit favourable clear and scattering states and favourableswitching and electro-optical performance.

No undesirable off-axis colour effects are observed.

The invention claimed is:
 1. A window element, which is operable in andelectrically switchable between an optically transparent state and ascattering state and which comprises a switching layer containing amaterial which comprises a liquid-crystalline medium comprising one ormore mesogenic compounds and one or more chiral compounds, wherein theliquid-crystalline medium has a clearing point of 95° C. or more, and apolymeric component comprising one or more polymeric structures obtainedby polymerization of one or more polymerizable mesogenic compounds inthe liquid-crystalline medium, wherein the polymeric component iscontained in the liquid-crystalline material in an amount, based on theoverall contents of the material, of 5% by weight or less, wherein thepolymeric component comprises a polymer network in theliquid-crystalline medium, and wherein in the optically transparentstate the window element has a haze, determined according to ASTM D1003, of less than 10%.
 2. The window element according to claim 1,wherein the liquid-crystalline medium contains, based on the overallcontents of the medium, at least 15% by weight of one or more mesogeniccompounds of formula I

wherein R¹ and R² denote, independently of one another, a group selectedfrom F, Cl, CF₃, OCF₃, and straight-chain or branched alkyl or alkoxyhaving up to 15 carbon atoms or straight-chain or branched alkenylhaving up to 15 carbon atoms which is unsubstituted, monosubstituted byCN or CF₃ or mono- or polysubstituted by halogen and wherein one or moreCH₂ groups may be, in each case independently of one another, replacedby —O—, —S—, —CO—, —COO—, —OCO—, —OCOO— or —C≡C— in such a manner thatoxygen atoms are not linked directly to one another, A¹¹ denotes

n denotes 0 or 1, and A²¹, A³¹ and A⁴¹ denote, independently of oneanother,

wherein L is on each occurrence, identically or differently, halogenselected from F, Cl and Br.
 3. The window element according to claim 1,wherein the liquid-crystalline medium further comprises one or moremesogenic compounds selected from the group of compounds of formulae IIand III

wherein R³, R⁴, R⁵ and R⁶ denote, independently of one another, a groupselected from F, CF₃, OCF₃, CN, and straight-chain or branched alkyl oralkoxy having up to 15 carbon atoms or straight-chain or branchedalkenyl having up to 15 carbon atoms which is unsubstituted,monosubstituted by CN or CF₃ or mono- or polysubstituted by halogen andwherein one or more CH₂ groups may be, in each case independently of oneanother, replaced by —O—, —S—, —CO—, —COO—, —OCO—, —OCOO— or —C≡C— insuch a manner that oxygen atoms are not linked directly to one another,and L¹, L², L³, L⁴ and L⁵ denote, independently of one another, H or F.4. The window element according to claim 1, wherein theliquid-crystalline medium exhibits a positive dielectric anisotropy Δεand an optical anisotropy Δn, determined at 20° C. and 589 nm, of 0.13or more, and wherein the one or more chiral compounds contained in theliquid-crystalline medium have an absolute value of the helical twistingpower of 5 μm⁻¹ or more.
 5. A method for preparing a window element ofclaim 1, comprising (i) providing said liquid-crystalline medium whichcomprises one or more mesogenic compounds, said one or more chiralcompounds, and said one or more polymerizable mesogenic compounds as alayer between two opposing transparent substrates which are eachprovided with an electrode, wherein the liquid-crystalline medium has aclearing point of 95° C. or more and exhibits a pitch of 0.55 μm ormore, and wherein the one or more polymerizable mesogenic compounds arecontained in the liquid-crystalline medium in an amount, based on theoverall contents of the medium, of 5% by weight or less, and (ii)polymerizing the one or more polymerizable mesogenic compounds in thepresence of an applied electric field in the layer to form the polymernetwork, wherein the polymerizing is carried out by photopolymerizationand wherein the applied electric field induces a homeotropic alignment,wherein subsequent to step (ii) a thermal treatment is carried out inthe presence or absence of an electric field.
 6. The method according toclaim 5, wherein the electrodes are arranged as conductive layers abovethe inner surface of each substrate.
 7. A window element for themodulation of the passage of light, wherein the window element isobtained by or obtainable from carrying out the method according toclaim
 5. 8. The window element according to claim 1, which is switchableinto the optically transparent state by applying an AC voltage V1 andwhich is switchable into the scattering state by applying an AC voltageV2, wherein V1>V2.
 9. The window element according to claim 1, whereinthe liquid-crystalline medium exhibits a pitch of 0.55 μm or more in thescattering state.
 10. A liquid-crystalline medium, comprising one ormore mesogenic compounds, one or more chiral compounds, one or morepolymerizable mesogenic compounds in an amount, based on the overallcontents of the medium, of 5% by weight or less, wherein the mediumexhibits a pitch of 0.55 μm or more and a clearing point of 95° C. ormore, and wherein the medium comprises a compound having the formula


11. The medium according to claim 10, which contains, based on theoverall contents of the medium, at least 15% by weight of one or moremesogenic compounds of formula I,

wherein R¹ and R² denote, independently of one another, a group selectedfrom F, Cl, CF₃, OCF₃, and straight-chain or branched alkyl or alkoxyhaving up to 15 carbon atoms or straight-chain or branched alkenylhaving up to 15 carbon atoms which is unsubstituted, monosubstituted byCN or CF₃ or mono- or polysubstituted by halogen and wherein one or moreCH₂ groups may be, in each case independently of one another, replacedby —O—, —S—, —CO—, —COO—, —OCO—, —OCOO— or —C≡C— in such a manner thatoxygen atoms are not linked directly to one another, A¹¹ denotes

n denotes 0 or 1, and A²¹, A³¹ and A⁴¹ denote, independently of oneanother,

wherein L is on each occurrence, identically or differently, halogenselected from F, Cl and Br, which optionally further comprises one ormore photoinitiators, and which optionally further comprises one or moremesogenic compounds selected from the group of compounds of formulae IIand Ill

wherein R³, R⁴, R⁵ and R⁶ denote, independently of one another, a groupselected from F, CF₃, OCF₃, CN, and straight-chain or branched alkyl oralkoxy having up to 15 carbon atoms or straight-chain or branchedalkenyl having up to 15 carbon atoms which is unsubstituted,monosubstituted by CN or CF₃ or mono- or polysubstituted by halogen andwherein one or more CH₂ groups may be, in each case independently of oneanother, replaced by —O—, —S—, —CO—, —COO—, —OCO—, —OCOO— or —C≡C— insuch a manner that oxygen atoms are not linked directly to one another,and L¹, L², L³, L⁴ and L⁵ denote, independently of one another, H or F.12. The medium according to claim 10, wherein one or more of the one ormore polymerizable mesogenic compounds comprise one, two or moreacrylate and/or methacrylate groups.
 13. A modulation material,comprising a liquid-crystalline medium comprising one or more mesogeniccompounds and one or more chiral compounds, wherein theliquid-crystalline medium has a clearing point of 95° C. or more andexhibits a pitch of 0.55 μm or more, and a polymeric componentcomprising one or more polymeric structures obtained by or obtainablefrom polymerization of one or more polymerizable mesogenic compounds,wherein the polymeric component is contained in the material in anamount, based on the overall contents of the material, of 5% by weightor less, wherein the polymeric component comprises a polymer network,wherein the liquid-crystalline medium exhibits a positive dielectricanisotropy Δε and an optical anisotropy Δn, determined at 20° C. and 589nm, of 0.13 or more, and wherein the one or more chiral compoundscontained in the liquid-crystalline medium have an absolute value of thehelical twisting power of 5 μm⁻¹ or more.
 14. A switching layer,comprising the medium according to claim
 10. 15. A switching layer,comprising the medium according to claim
 11. 16. The method according toclaim 6, wherein the conductive layers are arranged on a passivationlayer.
 17. The method according to claim 6, wherein the conductivelayers are arranged between passivation layers.
 18. The method accordingto claim 6, wherein alignment layers are provided which are in directcontact with the liquid-crystalline medium.
 19. The modulation materialaccording to claim 13, wherein the medium comprises a compound havingthe formula


20. The window element according to claim 1, wherein the polymericcomponent stabilizes one or more states of the liquid-crystallinemedium.
 21. The window element according to claim 1, wherein in thescattering state the window element has a haze, determined according toASTM D 1003, of more than 75%.